The International Glossary on Infertility and Fertility Care, 2025

Importance: Previous editions of the International Glossary on Infertility and Fertility Care (2006, 2009, 2017) established internationally recognized definitions related to clinical practice, research, and policy. The 2017 edition comprised 283 terms and, among many other changes, expanded the definition of infertility to include not only its recognition as a disease causing disability, but also as resulting from an impairment of a person’s capacity to reproduce either as an individual or with his/her partner.

The glossary has been extensively used worldwide and has contributed to international standardization of data collection, appropriate comparison of outcome measures, and provided a reference for all stakeholders, including policy makers. Updates are now required to reflect contemporary scientific knowledge, social needs, and inclusive definitions, while harmonizing international communication across clinical, research, policy, and public domains

Objective: To update the latest International Glossary on Infertility and Fertility Care, 2017 to reflect current scientific knowledge, evolving social contexts, and inclusive terminology, thereby promoting harmonized international communication across clinical, research, policy, and public domains.

Evidence review: Under guidance of the organizing committee, 21 professionals from across the world representing expertise in different sub-specialties formed five working groups: clinical definitions; outcome measures; embryology laboratory; clinical and laboratory andrology; and epidemiology, public health and gender related definitions. The definitions from the previous glossary were evaluated and new terms identified. All definitions were then reviewed by an international advisory panel of nine experts that evaluated the glossary from scientific, ethical, cultural, and policy perspectives. Following several virtual discussions and a one-day in-person meeting, most terms and definitions were agreed. In the absence of agreement, further discussions were held between the organizing committee, working group chairs and members of the advisory panel. It had been determined at the outset that final disagreement would be resolved via a two-thirds majority vote. All terms and definitions were, however, reached by consensus and adopted following a final round of review and approval by all authors.

Findings: The glossary now includes 348 terms. Compared to the previous edition, 14 terms were deleted, numerous terms were modified and 79 new terms were added. Modifications reflect current scientific knowledge, technological advancements, and inclusivity related to gender and family structures.

Conclusions and relevance: This updated glossary provides a global reference for standardized terminology, supporting clinical care, research, international comparisons, policy making, patient communication, and reproductive health literacy. Periodic updates will be required as scientific and societal contexts evolve. (Fertil Steril ® 2026;■:■–■. ©2026 by American Society for Reproductive Medicine.)

INTRODUCTION

Terms and definitions used in infertility and fertility care continue to evolve alongside rapid scientific progress and societal change. Clear, scientifically accurate, and internationally agreed terminology and definitions matter for many reasons. They facilitate the collection and comparison of scientific data nationally, regionally, and internationally. They are central for the scientific communication related to procedures and their outcomes to patients, health care providers, policy makers, and the wider public. Furthermore, they carry weight in shaping societal acceptance. For example, how the international scientific community defines an embryo, informed by the science of developmental biology, or defines infertility, not only guides scientific discourse but also influences legislation, policy making, funding priorities, and the promotion and protection of reproductive health and rights, especially for women and men suffering from infertility (1, 2). Lastly, they help to counter the current epidemic of misinformation and disinformation which, though having many drivers, thrives in the presence of ambiguity.

The first internationally standardized set of 53 definitions was published in 2006 by the International Committee for Monitoring Assisted Reproductive Technologies (ICMART) as The ICMART Glossary on ART Terminology (3, 4). In 2009, a revised edition including 87 definitions was published following an international consensus process led by ICMART in collaboration with the World Health Organization (WHO). This 2nd edition, now known as the WHO Glossary on Infertility, defined infertility for the first time as a disease of the reproductive system; a recognition and designation with wide-reaching social, legal, and financial implications (5, 6). The most recent edition, the International Glossary on Infertility and Fertility Care, 2017, comprising 283 definitions, was again published under the leadership of ICMART, in partnership with all major international organizations in the field (7, 8). In the 2017 edition, the definition of infertility was expanded in order to also recognize infertility as an impairment of function, thus widening the definition of infertility and bringing infertile persons and couples without a disease, as well as individuals and same sex couples under its umbrella. Many other terms were introduced for the first time, such as fertility awareness and fertility care, which are now used extensively in social science research.

Today, major advances in science and technology have reshaped both clinical practice and research. The use of new terminology in areas such as preimplantation genetic testing, whole-genome sequencing, and innovative methods for gamete and embryo assessment, require standardized definitions allowing for a proper evaluation of such procedures as well as the possibility of conducting national and international comparisons. Similarly, from a social science perspective, increasing access to fertility treatments by gender-diverse individuals requires new definitions which need to be precise, inclusive, and culturally accepted. Definitions that once assumed a binary, heteronormative framework are no longer sufficient to guide practice or policy in an era where reproductive autonomy and equity are central to human health and rights (9).

In this glossary on the science and biology of human reproduction, the terms female and male are used to refer to the biological sex, while recognizing that there is further biological diversity of sex. The words woman/women are used to refer to cisgender women (women born female and identifying as women) as well as gender-diverse persons with female reproductive organs, while equally recognizing all women in their biological and gender diversity. The words man/men are used to refer to cisgender men (men born male and identifying as men) as well as gender-diverse persons with male reproductive organs, while equally recognizing all men in their biological and gender diversity. We refer to a couple as two persons jointly intending to have a child, while acknowledging that some persons may be single parents and that some relationships may involve more than one partner.

This new edition of the International Glossary on Infertility and Fertility Care aims to provide an authoritative, evidence-based, and inclusive set of terms and definitions, aligned with the science and social needs of contemporary fertility care, and to continue harmonizing communication across disciplines and geographical regions.

WORKING METHODOLOGY

The development of this glossary followed a similar methodology as previous editions (5–8). Briefly, a structured, consensus-driven process designed to ensure scientific accuracy, inclusivity, and cultural sensitivity was implemented by ICMART. This process commenced with the invitation and appointment of two chairs for each of five working groups. In conjunction with these ten chairs, other leading experts in their field were invited to join, resulting in 21 experts with a maximum of five professionals per working group (Table 1). Some chairs and members had participated in the 2017 glossary edition, thus ensuring continuity, while others were new to this work. The working groups covered the following areas: (1) clinical definitions, (2) laboratory embryology, (3) clinical and laboratory andrology, (4) outcome measures and (5) epidemiology, public health, and gender-related terminology applicable to reproduction.

Led by the chairs, the working groups reviewed all definitions from the 2017 edition, deleting when relevant, recommending modifications where needed, and proposing new definitions in response to advances in science, clinical practice, and societal needs. Furthermore, special effort was made to ensure consistency with definitions already addressed by the World Health Organization (WHO) and included in the International Classification of Diseases (ICD-11).

Between November 2024 and June 2025, periodical virtual meetings were held within each working group and between individual working groups and the organizing committee. Some of these virtual meetings included members from all working groups.

All terms and definitions were then reviewed by an international advisory panel (IAP) comprising nine experts with global geographic distribution and representing most international and regional organizations responsible for infertility and fertility care (Table 1). Their role was to evaluate each term not only from a scientific perspective but also to consider ethical, cultural, and policy implications.

Subsequently, a one-day, in-person meeting was held at the 2025 ESHRE annual meeting with representatives of all working groups, the organizing committee, and members of the IAP. Each working group chair or representative presented their new terminologies as well as those which had been flagged for discussion by the advisory panel or the working group itself. In this manner, most of the meeting was utilized to discuss the more challenging terms and reach consensus. A few terms for which consensus could not be reached were flagged for further work and discussion together with addressing additional input from the advisory panel. Although it had been determined at the outset that any final disagreement would be resolved via a two-third majority vote, all definitions were ultimately reached by consensus. In September 2025, a pre-final document was distributed to all working group members and the advisory panel for acceptance or final comments. This feedback was incorporated upon which the final document for publication was generated and sent for review and endorsement by patient organizations.

This entire process was coordinated and overseen by the ICMART organizing committee, which facilitated communication across the working groups, consolidated revisions, and ensured alignment with the glossary’s overarching aims.

Table 1. Working group and International advisory panel members

Group	Name	Country/Organization
ICMART Organizing committee	F Zegers-Hochschild S Dyer GD Adamson	Chile South Africa USA
Clinical terminology working group	S Bhattacharya (chair) UKK Barnhart (chair) E Elgindy M Luna	UK USA Egypt Mexico
Laboratory terminology working group	C Racowsky (chair) FranceL Rienzi (chair) V Baker P Nagy LN Vuong D Wells	France Italy USA USA Vietnam UK
Andrology terminology working group	P Schlegel (chair) D Lamb (chair) MH Vazquez-Levin	USA USA Argentina
Outcome measures terminology working group	A Pinborg (chair) T Turner (chair) G Chambers SC Jwa M Kupka	Denmark Australia Australia Japan Germany
Epidemiology, public health, and gender related terminology working group	L Schmidt (chair) K Hammarberg (chair) B Monseur	Denmark Australia USA
International advisory panel	C Boothroyd J de Mouzon B Fauser M Horton O Ishihara M Khrouf G Martinez I Wada C Wyns	Australia France Netherlands Argentina Japan Tunisia Argentina Nigeria Belgium
ICMART, International Committee for Monitoring Assisted Reproductive Technologies.

The International Glossary on Infertility and Fertility Care, 2025

Term	Glossary definition 2025
Acrosome	A membrane-bound structure located at the front end of the sperm head, containing proteolytic enzymes necessary for penetration of the zona pellucida of the oocyte during fertilization.
Adenomyosis	A condition of the uterus characterized by endometrial tissue growth in the myometrium. Its confirmation is by histopathology and/or imaging (ultrasound and MRI).
Adhesions	Bands of fibrous scar tissue that may bind tissue of a same organ or a different organ, including the peritoneum, to each other. They can be dense and thick or filmy and thin. Adhesions involving abdominal/pelvic organs and the peritoneum can potentially influence fertility.
Age specific fertility rate (ASFR)	The number of live births per woman in a particular age group in a specific calendar year expressed per 1000 women in that age group.
Agglutination	The clumping of motile spermatozoa. It may be associated with the presence of anti-sperm antibodies or other factors which can impair sperm movement and fertilizing capacity.
Aggregation	The clumping of immotile spermatozoa and/or the adherence of spermatozoa to mucus strands, non-sperm cells or debris.
Andrology	The medical specialty that focuses on the scientific evaluation, causes and treatment of conditions affecting the male reproductive system and related disorders, including male infertility, sexual dysfunction and hormonal abnormalities.
Aneuploidy	An abnormal number of chromosomes in a cell. The majority of embryos that are uniformly aneuploid are not compatible with successful development and/or establishment of a viable pregnancy; such embryos are commonly referred to as aneuploid.
Anti-sperm antibodies	Antibodies that recognize and bind to antigens on the surface of the spermatozoon.
Artificial gametes	Gametes generated by in vitro manipulation of embryo-derived stem cells or somatic-induced pluripotent stem cells.
Aspermia	Lack of external ejaculation.
Assisted hatching	An ART technique in which the zona pellucida of an embryo is either thinned or perforated by chemical, mechanical, or laser methods.
Assisted reproductive technology (ART)	All interventions that involve the in vitro handling of both human oocytes and sperm, or of embryos, for the purpose of establishing a pregnancy. This includes, but is not limited to, in vitro fertilization and embryo transfer, intracytoplasmic sperm injection, embryo biopsy, preimplantation genetic testing, gamete and embryo cryopreservation, semen, oocyte and embryo donation, and gestational surrogacy cycles. (Thus ART does not, and ART-only registries do not, include intra-uterine/intra-cervical insemination using sperm from either a woman's partner or a sperm donor). [See broader term, Medically Assisted Reproduction, MAR].
Asthenoteratozoospermia	Reduced percentages of motile and morphologically normal sperm in the ejaculate below the lower reference limit. When reporting results, the reference criteria should be specified.
Asthenozoospermia	Reduced percentage of motile sperm in the ejaculate below the lower reference limit. When reporting results, the reference criteria should be specified.
Atypical fertilization	A sequence of biological processes initiated by entry of a sperm(s) into a mature oocyte where the number of pronuclei is not two at the fertilization check. However, some of these atypically fertilized oocytes (previously referred to as "abnormal") may be diploid after self-correction by unknown events. These zygotes may be developmentally competent.
Autologous MAR cycle	A MAR cycle using both female and male gametes and/or embryos originating from the intended parents and in which gametes and/or embryo(s) is/are transferred to the female intended parent.
Autologous oocyte banking	A procedure in which autologous oocytes are retrieved, cryopreserved, and stored. Short-term banking is usually intended to result in embryo transfer in the near future. Longer term banking is also referred to as fertility preservation.
Azoospermia	The absence of spermatozoa in the ejaculate.
Azoospermia factor (AZF)	A region on the long arm of the Y chromosome containing genes important for normal spermatogenesis. Different sections of this region are referred to as AZFa, AZFb and AZFc.
Biochemical pregnancy	A pregnancy diagnosed only by the detection of beta hCG in serum or urine.
Birth (single)	The complete expulsion or extraction from a woman of a fetus after 22 completed weeks of gestation, irrespective of whether it is a live birth or stillbirth, or, if gestational age is unknown, a birth weight more than 500 grams. For the purpose of ART/MAR registries, a single birth refers to an individual newborn; a delivery of multiple births, such as a twin delivery, would be registered as two births.
Birth per embryo that is transferred	The number of births divided by the number of embryos transferred (usually expressed as percentage, %). It must be stated whether it includes only live births or all births.
Blastocentesis	Aspiration of blastocoele fluid, typically followed by molecular analysis with the aim of providing information on the genetic constitution of the embryo. This technique is referred to as "minimally invasive PGT".
Blastocoele	The fluid-filled central region of the blastocyst.
Blastocyst	The stage of embryo development that typically begins on day 5 or 6, but may be delayed to day 7. A blastocyst with normal morphology comprises a fluid-filled cavity bounded by an outer layer of cells (trophectoderm) and an inner cluster of cells (inner cell mass).
Blastocyst expansion	The increase in blastocyst volume resulting from the accumulation of fluid in the blastocoele, accompanied by thinning of the zona pellucida. Blastocyst expansion can be periodically interrupted by "collapse", a temporary reduction in volume.
Blastomere	A cell in a cleavage stage embryo through to completion of compaction. Blastomere symmetry: the extent to which all blastomeres are even in size and shape.
Blastulation	The process in which fluid accumulates between cells, ultimately to coalesce and form the blastocoele.
Blastulation rate	The number of blastocysts generated divided by the number of zygotes generated.
Cancelled ART cycle	An ART cycle in which ovarian stimulation or monitoring has been carried out with the intention to treat, but which did not proceed to follicular aspiration or in the case of a thawed or warmed embryo did not proceed to embryo transfer.
Childlessness	A condition in which a person, voluntarily or involuntarily, is not a legal or societally-recognized parent to a child, or has experienced the death of her/his/ their child(ren).
Chimerism	Presence in a single individual of two or more cell lines, each derived from different genotypes.
Chromatid	One of the two copies of a chromosome that has replicated prior to cell division. The two chromatids normally remain attached at the centromere until they separate during anaphase of the cell cycle.
Cis-gender	A term that refers to persons whose gender identity corresponds to the sex they were assigned at birth.
Cleavage stage embryos	Embryos beginning with the 2-cell stage and up to, but not including, the morula stage.
Clinical pregnancy	A pregnancy diagnosed by ultrasonographic visualization of one or more gestational sacs or definitive clinical signs of pregnancy. In addition to intrauterine pregnancy it includes a clinically documented ectopic pregnancy.
Clinical pregnancy rate	The number of clinical pregnancies expressed per 100 initiated cycles, aspiration cycles, or embryo transfer cycles. When clinical pregnancy rates are recorded, the denominator (initiated, aspirated, or embryo transfer cycles) must be specified.
Clinical pregnancy with fetal cardiac activity	A pregnancy diagnosed by ultrasonographic or clinical documentation of at least one fetus with discernible cardiac activity.
Cohort total fertility rate (CTFR)	The observed average number of live born children per woman applied to a birth cohort of women as they age through time. This is obtained from data on women after completing their reproductive years.
Compaction	The process during which tight junctions form between juxtaposed blastomeres, resulting in indistinguishable cell membranes by light microscopy.
Complex aneuploidies	Two or more aneuploidies involving different chromosomes in the embryo. When two or more autosomes are involved, this condition is not compatible with human life.
Congenital anomalies	Structural or functional disorders that occur during intrauterine life and can be identified prenatally, at birth or later in life. Congenital anomalies can be caused by single gene defects, chromosomal disorders, multifactorial inheritance, environmental teratogens and micronutrient deficiencies. The time of identification should be reported.
Congenital anomaly birth prevalence	The number of births exhibiting signs of congenital anomalies per 10,000 births. When recording individual births with congenital anomalies, the time of the identification of the anomaly should be documented.
Congenital bilateral absence of the Vasa Deferentia (CBAVD)	The absence, at birth, of both duct systems (vas deferens) that connect the epididymis to the ejaculatory duct. The condition is typically associated with cystic fibrosis transmembrane conductance regulator (CFTR) gene mutation or mesonephric anomalies. The epididymis is typically only present in the caput region. Although the testes usually develop and function normally, men present with low volume azoospermia.
Conventional in vitro insemination	The co-incubation of oocytes with sperm in vitro with the goal of resulting in extracorporeal fertilization.
Copy number variation (CNV)	The variation in the number of copies of a defined region of a chromosome/ specific DNA sequence. Such variation may be polymorphic and not necessarily pathogenic.
Corona radiata cells	The innermost cells of the cumulus oophorus.
Cross border reproductive care	The provision of reproductive health services in a different jurisdiction or outside of a recognized national border within which the person(s) seeking care legally reside.
Cryopreservation	The process of preserving biological material (e.g., gametes, zygotes, cleavage-stage embryos, morula, blastocysts or gonadal tissue), typically by vitrification or slow-freezing, at extreme low temperature.
Cryptorchidism	A condition in which one or both testes did not descend to the scrotal position and cannot be brought into the scrotum with palpation. Testicular descent normally occurs in the late fetal period and up to six months after birth. An undescended testis may result in progressive testicular dysfunction and increased risk of testicular cancer development.
Cumulative delivery with at least one live birth per aspiration/initiated cycle	The number of deliveries with at least one live birth resulting from one initiated or aspirated ART cycle, including all cycles in which fresh and/or frozen embryos are transferred, until one delivery with a live birth occurs or until all embryos are used, whichever occurs first. The delivery of a singleton, twin, or other multiples is registered as one delivery. In the absence of complete data, the cumulative delivery rate is often estimated.
Cumulus oophorus	The multi-layered mass of granulosa cells (cumulus cells) surrounding the oocyte.
Current ART cycle	An ART cycle intended to result in embryo transfer during the same cycle or shortly thereafter. It includes autologous and heterologous fresh and frozen cycles, including freeze all cycles and short-term autologous oocyte banking.
Cytoplasmic maturation	The process during which the oocyte acquires the capacity to support nuclear maturation, fertilization, pronuclei formation, syngamy and subsequent early cleavage divisions until activation of the embryonic genome.
Cytoplasmic strings	Thin, thread-like cytoplasmic projections that interconnect inner cell mass and trophectoderm cells in expanding/expanded blastocysts, typically seen by light microscopy.
Cytoplasmic transfer	A technique that can be performed at different stages of an oocyte's development to add to or replace a fraction of the cytoplasm with cytoplasm from a donor egg.
Decreased spermatogenesis	The histologic description in which spermatogenesis is present with few spermatogenic cells in the seminiferous tubules, resulting in a decreased number or absence of sperm in the ejaculate.
Deferred ART cycle	An ART cycle intended for the collection and storage of gametes or embryos for deferred use. It includes fertility preservation cycles and donor oocyte banking cycles.
Delayed ejaculation	A condition in which it takes a man an extended period of sexual arousal to reach orgasm and ejaculation.
Delivery	The complete expulsion or extraction from a woman of one or more fetuses, after at least 22 completed weeks of gestation, irrespective of whether they are live births or stillbirths. A delivery of either a single or multiple newborn is considered as one delivery. If more than one newborn is delivered, it is often recognized as a delivery with multiple births.
Delivery rate	The number of deliveries expressed per 100 initiated cycles, aspiration cycles, or embryo transfer cycles. When delivery rates are recorded, the denominator (initiated, aspirated, or embryo transfer cycles) must be specified. It includes deliveries that resulted in the birth of one or more live births and/or stillbirths. The delivery of a singleton, twin, or other multiple pregnancy is registered as one delivery. If more than one newborn is delivered, it is often recognized as a delivery with multiple births.
Diandric oocytes	An oocyte with an additional set of haploid chromosomes of paternal origin.
Digynic oocytes	An oocyte with an additional set of haploid chromosomes of maternal origin.
Diploidy	In humans, diploidy is a condition in which cells have two copies of each of the 22 autosomes as well as a pair of sex chromosomes. This is the chromosomally normal state.
Disomy	A normal number of copies of a chromosome in a cell, characterized by the presence of two homologous chromosomes.
Donor insemination	A MAR procedure of placing laboratory processed sperm or semen from a man into the reproductive tract of a woman who is not his partner, for the purpose of initiating a pregnancy.
Donor oocyte banking	A procedure in which donor oocytes are retrieved, cryopreserved, and stored for subsequent donation to third parties through assisted reproduction.
Double embryo transfer (DET)	The transfer of two embryos in an ART procedure. This may be elective (eDET) when more than two embryos of sufficient quality for transfer are available.
Early ejaculation	A condition in which semen is released sooner than desired during sexual activity (also known as premature ejaculation).
Early neonatal death/ mortality	Death of a live-born infant within 7 days of birth.
Early neonatal death/ mortality rate	The sum of early neonatal deaths, per 1000 live births. For the international comparison of early neonatal mortality rates, it is recommended to only include births after 28 completed weeks of gestation in the numerator and denominator.
Ectopic pregnancy	A pregnancy outside the uterine cavity, diagnosed by ultrasound, surgical visualization, or histopathology.
Ejaculation	The process of ejection of semen from the male reproductive system through the urethra, typically as a result of sexual stimulation. It comprises an emission phase (sperm and fluids from accessory glands are released into the prostatic urethra) and an expulsion phase (rhythmic contractions of muscles that propel semen out of the penis).
Ejaculation retardata	The persistent difficulty or inability to ejaculate despite the presence of adequate sexual desire, erection, and stimulation.
Ejaculatory duct	The paired canals that are formed from the coalescence of the vas deferens and the seminal vesicle on each side. It passes posteriorly through the prostate and terminates on the lateral sides of the verumontanum.
Elective single embryo transfer (eSET)	The transfer of one embryo selected from a larger cohort of available embryos.
Embryo	The biological organism resulting from the development of the zygote, until eight completed weeks after fertilization, equivalent to 10 weeks of gestation.
Embryo bank	Repository of cryopreserved embryos.
Embryo cryopreservation	The process of preserving embryos at extreme low temperature, typically by vitrification.
Embryo donation	The use of embryos by individuals other than their progenitors for reproductive or research purposes.
Embryo donation recipient cycle	An ART cycle in which a woman receives one or more embryos resulting from donated male and female gametes.
Embryo fragmentation	The process during which one or more blastomeres exocytose membrane vesicles containing cytoplasm and occasionally whole chromosomes or chromatin. These fragments may subsequently be endocytosed.
Embryo transfer (ET)	The procedure of placing one or more preimplantation embryos at any embryonic stage from day 1 to day 7 into the uterus. (Embryos from day 1 to day 3 can also be transferred into the Fallopian tube, though this is rarely indicated).
Embryo transfer cycle	An ART cycle in which one or more fresh, frozen-thawed, or vitrified-warmed embryos are transferred into the uterus.
Embryo-like structure	Structures derived from embryonic or induced pluripotent stem cells, including synthetic embryos, stem-cell embryo models, and stem-cell-derived embryos. Such structures may be integrated (i.e., contain all cell types required for both fetal and extraembryonic tissue development) or non-integrated (i.e., lack one or more tissue type).
Emission (semen)	The release of semen into the urethra resulting from coordinated contractions of the vas deferens, seminal vesicles, and ejaculatory ducts. Additional fluid is released directly from prostatic glands into the urethra, also under autonomic control. Normally this event occurs immediately prior to the expulsion phase of ejaculation.
Endometrial preparation	Medical approaches used to prepare the endometrial lining to achieve optimal receptivity for embryo implantation of frozen-thawed or vitrified-warmed embryo transfer cycles. This is currently accomplished using natural, modified natural, hormone stimulation, and hormone replacement protocols.
Endometriosis	A disease characterized by the presence of endometrium-like epithelium and stroma outside the endometrium and myometrium. Intrapelvic endometriosis can be located superficially on the peritoneum (peritoneal endometriosis), can extend 5 mm or more beneath the peritoneum (deep endometriosis) or can be present as an ovarian endometriotic cyst (endometrioma).
Epididymis	A convoluted, highly coiled duct that transports the spermatozoa from the testis via the efferent ducts to the vas deferens.
Erectile dysfunction	Inability to have and/or sustain a penile erection sufficient for satisfactory sexual activity.
Euploidy	The condition in which a cell has chromosomes in an exact multiple of the haploid number; in the human this multiple is normally two. Thus, a chromosomally normal embryo is euploid and also diploid.
Excessive ovarian response	An exaggerated response to ovarian stimulation characterized by the development of more follicles than intended.
Expectant fertility management	Management of fertility problems without any specific active clinical or therapeutic interventions other than fertility information and advice, to improve natural fertility, based upon probability of becoming pregnant.
Extremely low birth weight	Birth weight less than 1000 g.
Extremely preterm birth	A birth that takes place after 22 but before 28 completed weeks of gestation.
Fecundability	The probability of a pregnancy, during a single menstrual cycle in a woman with adequate exposure to sperm and no contraception, culminating in a live birth. In population-based studies, fecundability is frequently measured as the monthly probability.
Fecundity	The capacity to have a live birth.
Female infertility	Infertility caused by female factors. These include ovulatory disturbances; low ovarian reserve; anatomical, endocrine, genetic, functional or immunological abnormalities of the reproductive system; chronic illness; and sexual conditions incompatible with coitus.
Fertility	The capacity to establish a clinical pregnancy (clinical definition). The capacity to deliver a liveborn child (demographic definition).
Fertility awareness	The understanding of human reproduction and related individual risk factors (e.g., advanced age, sexual health factors such as sexually transmitted infections, life style factors such as smoking, obesity) and non-individual risk factors (e.g., environmental, work place, societal and cultural factors) affecting people's ability to achieve their reproductive goals.
Fertility care	Interventions that include fertility awareness, support, and fertility management with an intention to assist individuals and couples to realize their reproductive goals.
Fertility preservation	Various interventions, procedures and technologies, including freezing of gametes, embryos or ovarian and testicular tissue to preserve reproductive capacity.
Fertilization	A sequence of biological processes initiated by entry of a spermatozoon into a mature oocyte followed by formation of the pronuclei.
Fetal death	The death of a fetus prior to birth, irrespective of the duration of pregnancy but after 10 completed weeks of gestation.
Fetus	The stage of development of an organism that begins at the end of the 8th completed week after fertilization (approximately 10 weeks of gestation) and continues until birth.
Freeze-all cycle	An ART cycle, in which, after oocyte aspiration, all oocytes and/or embryos are frozen and no embryos are transferred in that cycle.
Fresh embryo transfer cycle	An ART procedure in which cycle monitoring is carried out with the intention of transferring one or more embryos that were not previously cryopreserved. This includes embryos from the fertilization of frozen-thawed or vitrified-warmed oocytes. Note: A fresh embryo transfer cycle is initiated when specific medication is provided or cycle monitoring is started in the woman with the intention to treat.
Frozen-thawed embryo transfer cycle (FET)	An ART procedure in which cycle monitoring is carried out with the intention of transferring one or more frozen-thawed embryos. Note: An FET cycle is initiated when specific medication is provided or cycle monitoring is started in the woman with the intention to treat.
Frozen-thawed oocyte cycle	An ART procedure in which cycle monitoring is carried out with the intention of fertilizing frozen-thawed oocytes and performing an embryo transfer. Note: A frozen-thawed oocyte cycle is initiated when specific medication is provided or cycle monitoring is started in the woman with the intention to treat.
Gamete intrafallopian transfer (GIFT)	An ART procedure in which both gametes (oocytes and spermatozoa) are transferred into the Fallopian tubes.
Gender	A term that refers to the socially constructed roles, behaviours, expressions, and identities assigned for individuals based on the sex assigned at birth.
Gender dysphoria	A state of distress or discomfort that may occur when a person's gender identity differs from the sex assigned at birth.
Gender identity	A term that refers to how individuals perceive themselves with respect to their own gender, which may or may not align with the sex they were assigned at birth.
Gender transition	A process whereby people usually change from the gender expression associated with their assigned sex at birth to another gender expression that better matches their gender identity. This process is dynamic, reflecting the evolving and personal nature of each case.
Gender-affirming hormone therapy (GAHT)	Hormonal therapy to change primary and/or secondary sex characteristics with the aim to affirm a person's gender identity.
Gender-affirming surgery (GAS)	Surgery to change primary and/or secondary sex characteristics with the aim to affirm a person's gender identity.
Genome editing	A technique that changes the DNA of a cell or organism by adding, removing, or altering specified DNA sequences. Today, the most well-known technique for gene editing is the CRISPR-Cas9 system.
Germinal vesicle (GV)	The nucleus in an oocyte at prophase of meiosis I.
Gestational age	The duration of pregnancy calculated by the best obstetric estimate determined by all perinatal factors and assessments which may include last menstrual period, early ultrasound, and/or day of ovulation triggering. In the case of ART, it is calculated by adding 2 weeks (14 days) to the number of completed weeks since in vitro insemination or ICSI. (Note: For frozen-thawed embryo transfer (FET) cycles, an estimated date of insemination/ICSI is computed by subtracting the combined number of days an embryo was in culture pre-freeze and post-thaw, from the transfer date of the FET cycle).
Gestational sac	A fluid-filled structure associated with early pregnancy, which may be located inside or, in the case of an ectopic pregnancy, outside the uterus.
Gestational surrogacy	An ART procedure in which an embryo which has originated from the gametes of intended parent(s) and/or a third party (or parties) is transferred to the uterus of another woman with an agreement that she will give the offspring to the intended parent(s).
Gestational surrogate	A woman who carries a pregnancy with an agreement that she will give the offspring to the intended parent(s). Gametes can originate from the intended parent(s) and/or a third party (or parties). This term is also referred to as gestational carrier.
Globozoospermia	Structural defect of the spermatozoon characterized by a round head and the presence of an atrophied or absent acrosome.
Haploidy	The condition in which a cell has one set of each chromosome. In humans, this is characterized by the presence of 23 single chromosomes, which normally involves a single copy of each of the 22 autosomes and one sex chromosome. Mature human gametes are haploid.
Hatching	The process by which an embryo at the blastocyst stage extrudes out of, and ultimately separates from, the zona pellucida.
Heterotopic pregnancy	Concurrent pregnancy involving at least one embryo implanted in the uterine cavity and at least one implanted outside of the uterine cavity.
High-order multiple births	The complete expulsion or extraction from their mother of three or more fetuses, after 22 completed weeks of gestation, irrespective of whether they are live births or stillbirths.
High-order multiple gestation	A pregnancy with three or more embryos or fetuses.
Hydrosalpinx	A distally occluded, dilated, fluid-filled Fallopian tube.
Hypergonadotropic hypogonadism	Gonadal failure associated with reduced gametogenesis, reduced gonadal steroid production, and elevated gonadotropin production.
Hyperspermia	High volume of ejaculate above the upper reference limit. When reporting results, the reference criteria should be specified.
Hypogonadotropic hypogonadism	Gonadal failure associated with reduced gametogenesis and reduced gonadal steroid production due to reduced gonadotropin production or action.
Hypospermatogenesis	The histologic description of the testis where all the cellular elements of the seminiferous epithelium are present but at reduced cellularity.
Hypospermia	Low volume of ejaculate below the lower reference limit. When reporting results, the reference criteria should be specified.
Iatrogenic testicular failure	Damage to testicular function after a medical intervention such as radiation, chemotherapy, hormone treatment; or surgery (that may cause devascularization, such as after inguinal hernia surgery).
Identifiable donor	A person who is willing to donate his/her/their gametes or embryos for reproductive purposes, and accepts that his/ her/their identity can be revealed to the person born.
Immature oocyte	An oocyte that has not yet completed its final stages of maturation, which is typically at the germinal vesicle (GV) or metaphase I (MI) stage.
Implantation	The attachment and subsequent penetration by a zona-free blastocyst into the endometrium, but when it relates to an ectopic pregnancy, into tissue outside the uterine cavity. This process starts 5 to 7 days after fertilization of the oocyte, usually resulting in the formation of a gestational sac.
Implantation rate	The number of gestational sacs observed divided by the number of embryos transferred (usually expressed as a percentage, %).
In vitro fertilization (IVF)	A sequence of procedures that involves fertilization of gametes outside the body.
In vitro oocyte maturation (IVM)	A sequence of laboratory procedures that aims to enable immature cumulus-enclosed oocytes to mature into metaphase II oocytes outside the body. These oocytes are capable of being fertilized with potential to develop into embryos.
Indices of multiple sperm defects	Assessment of the incidence of different types of morphological abnormalities in spermatozoa, including the head, midpiece and principal piece in a multiple-entry system. They include: teratozoospermia index (TZI), multiple anomalies index (MAI) and sperm deformity index (SDI) and a combination of all three of these analyses with an additional assessment of sperm with excess residual cytoplasm.
Induced abortion	Intentional loss of an intrauterine pregnancy, through intervention by medical, surgical, or unspecified means.
Induced embryo/fetal reduction	An intervention intended to reduce the number of gestational sacs or embryos/fetuses in a multiple gestation.
Infertility	A disease characterized by the failure to establish a clinical pregnancy after 12 months of regular, unprotected sexual intercourse or due to an impairment of a person's capacity to reproduce either as an individual or with her/his/their partner. Infertility generates disability as an impairment of function. Fertility interventions may be initiated in less than 12 months based on medical, sexual and reproductive history, age, physical findings and diagnostic testing.
Infertility counselling	A professional intervention with the intention to mitigate the physical, emotional, and psychosocial consequences of infertility.
Initiated Medically Assisted Reproduction cycle (iMAR)	A MAR cycle in which the woman receives medication for ovarian stimulation/ ovulation induction or an embryo transfer cycle, and/or in which cycle monitoring is carried out, with the intention to treat.
Inner cell mass	A group of cells attached to the polar trophectoderm consisting of embryonic stem cells which have the potential to develop into all cells and tissues in the human body, except the placenta or amniotic membranes.
Intended parent(s)	Individuals or couples who have expressed their intention to become parents with the use of MAR.
Intersex	A term that refers to persons born with sex or reproductive characteristics that do not fit binary definitions of female or male.
Intra-cervical insemination	A procedure in which laboratory processed sperm are placed in the cervix to attempt a pregnancy.
Intra-uterine insemination	A procedure in which laboratory processed sperm are placed in the uterus to attempt a pregnancy.
Intra-uterine pregnancy	A state of reproduction in which an embryo has implanted in the uterus.
Intra-vaginal insemination	A procedure in which semen is placed in the vagina to attempt a pregnancy.
Intracytoplasmic morphologically selected sperm injection (IMSI)	Selection of sperm at higher magnification than for conventional ICSI to evaluate the integrity of the nucleus and allow intracytoplasmic injection of a more morphologically normal sperm (e.g., with less or no nuclear vacuoles).
Intracytoplasmic sperm injection (ICSI)	A technique in which a single spermatozoon is injected into the oocyte cytoplasm.
Ion channel/transporter evaluation	Tests that focus on how specific channels and transporters in sperm membranes affect motility, fertilization, and overall fertility. These tests include evaluation of CatSper (a Ca2+ channel), KSper/SLO3 (a K+ channel), and Hv1 (a proton channel).
Kallman syndrome	A condition, commonly genetic in origin, characterized by the presence of hypogonadotropic hypogonadism in association with midline defects (such as anosmia, cleft palate, or cleft lip).
Karyotype	A description of the chromosomal status of a sample consisting of a cell or cells, comprising the number of copies of each chromosome and indicating whether any rearrangements of chromosomal material have been detected (e.g., translocations, deletions/duplications, or inversions).
Klinefelter syndrome	A condition in males caused by the presence of one or more extra X chromosomes (typically 47,XXY) associated with impaired testicular development and function, that may also be associated with other systemic abnormalities. Hypogonadism is present in the majority of affected males.
Laparoscopic ovarian drilling	A surgical method for inducing ovulation in women with anovulatory or oligoovulatory cycles associated with polycystic ovaries, utilising either laser or electrosurgery.
Large for gestational age	A birth weight greater than the 90th percentile of the sex-specific birth weight for a given gestational age reference. When reporting outcomes, the reference criteria should be specified. If gestational age is unknown, then the birth weight should be registered.
Leukocytospermia	A high number of white blood cells in semen above the upper reference limit. A synonymous term is pyospermia. When reporting results, the reference criteria should be specified.
Leydig cell	A cellular element within the testis, located in the interstitial space between seminiferous tubules, that produces testosterone.
Live birth	The complete expulsion or extraction from a woman of a fetus after 22 completed weeks of gestation; which, after such separation, breathes or shows other signs of life, such as heart beat, umbilical cord pulsation, or definite movement of voluntary muscles, irrespective of whether the umbilical cord has been cut or the placenta is attached. A birth weight of 500 grams or more can be used if gestational age is unknown. Live birth refers to the individual newborn. A twin delivery represents two live births.
Live birth delivery rate	The number of deliveries that resulted in at least one live birth, expressed per 100 cycles. In the case of MAR/ART interventions, they can be initiated cycles, insemination cycles, aspiration cycles, or embryo transfer cycles. When delivery rates are given, the denominator (initiated, inseminated, aspirated, or embryo transfer cycles) must be specified.
Low birth weight	Birth weight less than 2500 g.
Low ovarian reserve	A biological term used to indicate a reduced number of primordial follicles in the ovaries. Clinically, low ovarian reserve may be determined indirectly by: a reduced number of antral follicles on ultrasound; low anti-Müllerian hormone levels; and reduced response to current or prior ovarian stimulation.
Low ovarian response to ovarian stimulation	A condition in which ≤3 follicles and/or oocytes are developed/obtained following ovarian stimulation with the intention of obtaining more follicles and/ or oocytes (also known as poor ovarian response). The risk of low ovarian response is increased in women who meet at least two of the following criteria: 1) age ≥40 years; 2) a previous low ovarian response and, 3) an abnormal ovarian reserve test, as measured by the number of antral follicles and/or anti-Müllerian Hormone levels. These measurements should be accompanied by a reference value obtained from a standard normal population.
Luteal phase defect	A poorly defined abnormality of the endometrium presumably due to abnormally low progesterone secretion or action on the endometrium.
Luteal phase support	Hormonal supplementation in the luteal phase, usually progesterone.
Magnetic activated sperm separation	A technique using a magnetic field to separate sperm labelled with specific surface markers from those unlabelled. This technique may be used for a variety of reasons, for example to separate non-apoptotic sperm from apoptotic sperm.
Major congenital anomaly	A congenital anomaly that requires surgical repair of a defect, is a visually evident or life-threatening structural or functional defect, or causes death.
Male infertility	Infertility caused by male factors. These include abnormal semen parameters or function; anatomical, endocrine, genetic, functional or immunological abnormalities of the reproductive system; chronic illness; and sexual conditions incompatible with the ability to deposit semen in the vagina.
Maternal age effect	The relationship between the female progenitor's age, at the time when gametes were generated, on the reproductive outcome and the health effects in the offspring. The age of the pregnant woman can further influence the health of the offspring and her own health. This term is also referred to as female progenitor age effect.
Maternal spindle transfer	Transfer of the maternal spindle (including maternal chromosomes) from a patient's oocyte into a donated oocyte in which the original spindle including chromosomes has been removed.
Mature oocyte	An oocyte capable of being fertilized.
Medically assisted reproduction (MAR)	Reproduction brought about through various interventions, procedures, surgeries and technologies to treat infertility. These include ovulation induction, ovarian stimulation, ovulation triggering, all ART procedures, uterine transplantation and intrauterine, intracervical, and intravaginal insemination with semen of husband/partner or donor.
Microdissection testicular sperm extraction (MicroTESE)	A surgical procedure using an operating microscope to identify seminiferous tubules that may contain sperm to be used for ICSI.
Microfluidic sperm separation	A technique through which small volumes of semen are subjected to laminar flow in a microchannel device to facilitate purification of a semen sample enriched with motile sperm.
Micromanipulation in ART	A micro-operative ART technique performed on sperm, egg or embryo. Examples of ART micromanipulation procedures are ICSI, assisted hatching, polar body biopsy, and embryo biopsy for PGT.
Micronucleus	A tiny nucleus in the cytoplasm of a cell, containing one or a few chromosomes or chromosome fragments (which may result in aneuploidy).
Microsurgical epididymal sperm aspiration/ extraction (MESA/MESE)	A surgical procedure performed with the assistance of an operating microscope to retrieve sperm from the epididymis of men with obstructive azoospermia.
Mild ovarian stimulation for ART	A protocol in which the ovaries are stimulated with gonadotropins and/or other pharmacological compounds with the deliberate intention of producing a limited number of oocytes for ART.
Miscarriage rate	The number of miscarriages/ spontaneous abortions per 100 clinical pregnancies with known pregnancy outcome. In a twin pregnancy, the loss of two embryos is counted as one miscarriage. The intrauterine loss of one embryo from a multiple gestation is not a miscarriage.
Missed abortion/missed miscarriage	Spontaneous arrest of a clinical pregnancy before 22 completed weeks of gestation, in which the embryo(s) or fetus(es) is/are nonviable and is/are not spontaneously absorbed or expelled from the uterus.
Modified natural ART cycle	An ART procedure in which one or more oocytes are collected from the ovaries during a spontaneous reproductive cycle. Pharmacological compounds are administered with the sole purpose of blocking the spontaneous LH surge and/or inducing final oocyte maturation.
Monosomy	The loss of one of the two homologous chromosomes. Autosomal monosomies throughout all cells in an embryo are typically incompatible with continued development. Embryos with a sex chromosome monosomy can sometimes establish a pregnancy but the great majority do not result in a live birth.
Monozygotic twins	The development of twins commonly considered as genetically identical resulting from the division of a single fertilized oocyte (zygote) or embryo up to 14 days after fertilization.
Morula	An embryo formed after completion of compaction, typically 4 days after fertilization.
Mosaicism	A state in which an embryo is composed of two or more genetically distinct cell populations due to a mutation or chromosome segregation error occurring after the 1-cell stage. In the case of chromosomal mosaicism, more than one karyotypically distinct cell line is present.
Multinucleation	The presence of more than one nucleus in a cell. This phenomenon includes micronucleation.
Multiple birth	The complete expulsion or extraction from a woman of more than one fetus, after 22 completed weeks of gestation, irrespective of whether it is a live birth or stillbirth. Births refer to the individual newborn; for example, a twin delivery represents two births.
Multiple gestation	A pregnancy with more than one embryo or fetus, irrespective of their location.
Natural ART cycle	An unmedicated ART procedure in which the spontaneous reproductive cycle is monitored with the intention to time follicular aspiration, or the transfer of one or more frozen-thawed or vitrified-warmed embryos.
Necrozoospermia	The presence of limited or absent live sperm in the ejaculate.
Neonatal death/mortality	Death of a live born baby within 28 days of birth. This can be sub-divided into: 1) early, if death occurs in the first 7 days after birth; and 2) late, if death occurs between 8 and 28 days after birth.
Neonatal mortality rate	Number of neonatal deaths (up to 28 days) per 1000 live births.
Neonatal period	The period which commences at birth and ends at 28 completed days after birth.
Next generation sequencing (NGS)	A term covering several different technologies that permit the simultaneous sequencing of large numbers of DNA sequences (massively parallel sequencing). Potentially, millions of DNA fragments can be sequenced at the same time, allowing rapid sequencing of numerous loci, or whole genomes.
Non-identifiable donor	A person who is willing to donate his/her/their gametes or embryos for reproductive purposes without having his/her/their identity revealed to the person born.
Non-invasive PGT	A test performed to analyze the genetic material of an embryo without biopsy to remove cells. An example is analysis of cell-free DNA in spent culture medium.
Non-obstructive azoospermia	Absence of spermatozoa in the ejaculate due to spermatogenic failure at any stage of spermatogenesis.
Nuclear maturation	The process during which the oocyte resumes meiosis and progresses from prophase I to metaphase II.
Obstructive azoospermia	Absence of spermatozoa in the ejaculate due to occlusion of the ductal system.
Oligospermia	A term for low semen volume now replaced by hypospermia to avoid confusion with oligozoospermia.
Oligozoospermia	Low concentration of spermatozoa in the ejaculate. When reporting results, the reference criteria must be specified.
Oocyte	The female gamete (egg).
Oocyte aspiration	Ovarian follicular aspiration performed with the aim to retrieve oocytes, also known as oocyte pick-up.
Oocyte bank	Repository of cryopreserved oocytes.
Oocyte cryopreservation	The process of preserving oocytes, typically by vitrification, at extreme low temperature.
Oocyte donation	The use of oocytes from an egg donor for reproductive purposes or research.
Oocyte donation cycle	An ART cycle in which oocytes are collected from an egg donor for reproductive purposes or research.
Oocyte donation recipient cycle	An ART cycle in which a woman receives one or more embryos resulting from the fertilization of oocytes from a donor.
Oocyte maturation	The progression of an oocyte from the germinal vesicle stage to complete the first meiotic division and reach metaphase of the second division. This progression can occur through natural physiological events, or be induced in vivo or in vitro.
Oocyte/Embryo/Blastocyst biopsy	Removal of biological material from oocytes or embryos. This most commonly involves removal of polar body(ies) from oocytes, blastomere(s) from cleavage stage embryos, or trophectoderm cells from blastocysts. Biopsy specimens of these types provide the DNA used for preimplantation genetic testing (PGT).
Oolemma	The cytoplasmic membrane enclosing the oocyte.
Ooplasm	The cytoplasm of the oocyte.
Ovarian hyperstimulation syndrome (OHSS)	An exaggerated systemic response to ovarian stimulation characterized by a wide spectrum of clinical and laboratory manifestations. It may be classified as mild, moderate or severe according to the degree of abdominal distention, ovarian enlargement and respiratory, haemodynamic and metabolic complications.
Ovarian reserve	Biologically defined as the number of primordial follicles remaining in the ovaries. Clinically, this correlates indirectly to: the number of antral follicles on ultrasound; anti-Müllerian hormone levels; follicle stimulating hormone and estradiol levels; and response to current or prior ovarian stimulation. These tests can be used as surrogate markers of ovarian reserve.
Ovarian stimulation (OS)	Pharmacological treatment with the intention to induce the development of ovarian follicles. It can be used for two purposes: 1) for timed intercourse or insemination; 2) in ART, to obtain multiple oocytes at follicular aspiration.
Ovarian tissue cryopreservation	The process of preserving ovarian tissue, by slow freezing or vitrification, at extreme low temperature.
Ovarian tissue oocyte in vitro maturation (OTO-IVM)	A sequence of experimental laboratory procedures that aims to mature immature cumulus-enclosed oocytes obtained from slices of ovarian cortical tissue, so that they are capable of being fertilized with the potential to develop into embryos.
Ovarian torsion	Partial or complete rotation of the ovarian vascular pedicle that causes obstruction to ovarian blood flow, potentially leading to necrosis of ovarian tissue.
Ovulation	The natural process of expulsion of a mature egg from its ovarian follicle.
Ovulation induction (OI)	Pharmacological treatment of women with anovulation or oligo-ovulation with the intention of inducing an ovulatory cycle.
Ovulation trigger	Pharmacological treatment with the intention of inducing oocyte maturation and, in non-ART cycles, follicular rupture and oocyte expulsion.
Parthenogenetic activation	The process by which an oocyte is activated to undergo development in the absence of fertilization, also known as parthenogenesis.
Parthenote	The product of an oocyte that has been activated (either spontaneously or by artificial induction) to undergo development in the absence of the paternal genome.
Paternal age effect	The relationship between the male progenitor's age, at the time when gametes were generated, on the reproductive outcome and the health effects in the offspring. This term is also referred to as male progenitor age effect.
Percutaneous epididymal sperm aspiration (PESA)	A procedure in which a needle is introduced percutaneously into the epididymis with the intention of obtaining sperm.
Perinatal death/mortality	Fetal or neonatal death occurring during late pregnancy (after 22 completed weeks of gestation), during childbirth, or up to 7 completed days after birth.
Perinatal mortality rate	The number of perinatal deaths, per 1000 total births (stillbirths plus live births). When calculating a perinatal mortality rate, it must be specified if it includes both early and late gestation stillbirths or only late gestation stillbirths. For the international comparison of Perinatal Mortality Rates, it is recommended to only include late gestation stillbirths and only births after 28 completed weeks of gestation in the denominator.
Perinatal period	The period from 22 completed weeks of gestation to 7 completed days after birth.
Period total fertility rate (PTFR)	The estimated average number of live born children per woman that would be born to a cohort of women throughout their reproductive years, if the fertility rates by age in a given period remained constant as the current age-specific fertility rate.
Perivitelline space	The space between the cytoplasmic membrane enclosing the oocyte and the innermost layer of the zona pellucida. (This space may contain the first and second polar bodies and extracellular fragments).
PGT for aneuploidy (PGT-A)	A test performed to infer the chromosomal status of oocytes (via polar bodies) or embryos (typically via trophectoderm biopsy).
PGT for chromosomal structural rearrangements (PGT-SR)	A test performed to detect imbalances of chromosome material associated with inherited structural rearrangements in oocytes (via polar bodies) or embryos (typically via trophectoderm biopsy).
PGT for estimation of polygenic disease risk (PGT-P)	A test performed to estimate polygenic disease risk in embryos (typically via trophectoderm biopsy).
PGT for HLA matching (PGT-HLA)	A test performed to evaluate the suitability of an embryo (typically via trophectoderm biopsy) to serve as a tissue-matched (human leucocyte antigen (HLA) compatible) donor for a person requiring stem cell or organ transplantation.
PGT for monogenic/single gene defect (PGT-M)	A test performed to determine the presence of monogenic/single gene defects in oocytes (via polar bodies) or embryos (typically via trophectoderm biopsy).
Physiological intracytoplasmic sperm injection (PICSI)	A technique for selection of sperm bound to hyaluronic acid with the intention to inject a sperm with better DNA quality.
Pituitary down-regulation	A pharmacological method to prevent the release of gonadotropins (FSH, LH) from the pituitary gland.
Polar bodies	The small bodies containing chromosomes segregated from the oocyte by asymmetric division during telophase. The first polar body is extruded at telophase I and normally contains only chromosomes with duplicated chromatids (2c); the second polar body is extruded in response to fertilization or in response to parthenogenetic activation and normally contains chromosomes comprised of single chromatids (1c).
Polycystic ovarian syndrome (PCOS)	A heterogeneous condition, which requires the presence of two of the following three criteria: 1) Oligo-ovulation or anovulation; 2) Hyperandrogenism (clinical evidence of hirsutism, acne, alopecia and/or biochemical hyperandrogenaemia); 3) Polycystic ovarian morphology, as assessed by transvaginal ultrasound, consistent with ≥ 20 follicles and/or ovarian volume >10 ml in at least one ovary.
Polycystic Ovary (PCO)	Polycystic ovarian morphology, as assessed by transvaginal ultrasound, consistent with ≥ 20 follicles and/or ovarian volume >10 ml in at least one ovary.
Polygenic disease	A condition resulting from the combined effects of multiple genes, each having a relatively small contribution to the overall risk of developing disease, and often interacting with environmental factors.
Polyploidy	The condition in which a cell has more than two haploid sets of chromosomes; e.g., a triploid embryo has three sets of chromosomes; a tetraploid embryo has four sets. Polyploidy in a human embryo is not compatible with life.
Polyspermy	The process by which an oocyte is penetrated by more than one spermatozoon.
Post-term birth	A live birth or stillbirth that takes place after 42 completed weeks of gestation.
Posthumous reproduction	A process utilizing gametes and/or embryos from a deceased person or persons with the intention of producing an offspring.
Postimplantation embryo	A developing embryo after it has successfully attached to/implanted in the lining of the uterus to 8 completed weeks after fertilization which is equivalent to 10 weeks of gestation.
Pregnancy	A state of reproduction beginning with implantation of an embryo in a woman and ending with the complete expulsion and/or extraction of all products of implantation.
Pregnancy loss	The outcome of any pregnancy that does not result in at least one live birth. When reporting pregnancy loss, the estimated gestational age at the end of pregnancy should be recorded.
Pregnancy of unknown location (PUL)	A pregnancy documented by a positive human Chorionic Gonadotropin (hCG) test without visualization of pregnancy by ultrasound. This condition exists only after circulatory hCG is compatible with ultrasound visualization of a gestational sac.
Preimplantation embryo	Stages in development beginning with division of the zygote into two cells and ending just prior to implantation into a uterus.
Preimplantation genetic diagnosis (PGD) and screening (PGS)	Terms that have now been replaced by preimplantation genetic testing PGT (see PGT and the subtypes of PGT and their definitions).
Preimplantation genetic testing (PGT)	A test performed to analyze the genetic material in oocytes (via polar bodies) or embryos (typically via trophectoderm biopsy). These include: PGT for aneuploidies (PGT-A); PGT for monogenic/single gene defects (PGT-M); PGT for chromosomal structural rearrangements (PGT-SR); PGT for polygenic disease risk (PGT-P); and PGT for HLA matching (PGT-HLA).
Premature ovarian insufficiency (POI)	A clinical syndrome characterized by hypergonadotropic hypogonadism in women younger than age 40 (also known as premature or primary ovarian failure, or primary ovarian insufficiency, or premature menopause).
Preterm birth	A birth that takes place after 22 weeks and before 37 completed weeks of gestation.
Primary childlessness	A condition in which a person has never delivered a live child, or has never been a legal or societally-recognized parent to a child.
Primary female infertility	A condition in which a woman has never been diagnosed with a clinical pregnancy and meets the criteria of being infertile.
Primary involuntary childlessness	A condition in which a person with a wish for a child has never delivered a live child, or been a legal or societally-recognized parent to a child. A major cause of primary involuntary childlessness is infertility.
Primary male infertility	A condition in which a man has never contributed to a clinical pregnancy and meets the criteria of being infertile.
Progressive sperm motility	Sperm actively moving forward in a linear or large circular pattern.
Pronuclei transfer	Transfer of the pronuclei from a patient's zygote to an enucleated donated zygote.
Pronucleus	A spherical structure in the ooplasm containing chromatin and surrounded by a membrane. This structure forms after activation/fertilization.
Recipient (ART)	A person or couple who receives donated eggs, sperm, or embryos for the purposes of initiating a pregnancy.
Reciprocal IVF	A method of shared assisted reproduction and parenthood among two female partners. One provides the oocytes for the generation of embryos while the other undergoes embryo transfer with the intention of becoming pregnant.
Recurrent spontaneous abortion/ miscarriage	The spontaneous loss of two or more clinical pregnancies prior to 22 completed weeks of gestation.
Reproductive surgery	Surgical procedures performed to diagnose, conserve, correct, and/or improve reproductive function. Surgery for contraceptive purposes such as tubal ligation and vasectomy are also included within this term.
Rescue IVM (r-IVM)	A sequence of laboratory procedures that aims to mature in vitro cumulus-free immature oocytes obtained after ovarian stimulation and ovulatory trigger, so that they are capable of being fertilized with the potential to develop into embryos.
Retrograde ejaculation	A condition in which semen passes backward into the bladder after emission, associated with dysfunction of the sphincter at the bladder neck, resulting in a low volume or absent antegrade ejaculate.
Salpingectomy	The surgical removal of an entire Fallopian tube.
Salpingitis isthmica nodosa (SIN)	A nodular thickening of the proximal Fallopian tube (where the tubes join the uterus) which can distort or occlude the tubes. This condition increases the risk of ectopic pregnancy and infertility.
Salpingostomy	A surgical procedure in which an opening is made in the Fallopian tube either to remove an ectopic pregnancy or open a blocked fluid-filled tube (hydrosalpinx).
Secondary female infertility	A condition in which a woman is diagnosed as infertile following a previously confirmed clinical pregnancy.
Secondary involuntary childlessness	A condition in which a person with a wish for a child who previously delivered a live child, or is or has been a legal or societally-recognized parent to a child is unable to have a subsequent child. A major cause of secondary involuntary childlessness is infertility.
Secondary male infertility	A condition in which a man is diagnosed as infertile after having previously contributed to a confirmed clinical pregnancy.
Segmental aneuploidy	An abnormality involving loss or duplication of part of a chromosome (i.e., aneuploidy affecting a segment of a chromosome).
Semen analysis	A descriptive assessment of the ejaculate to assess functions of the male reproductive tract. Characteristic parameters include liquefaction, volume, viscosity, odour, colour and opalescence of the semen, presence of agglutination or aggregation of the sperm, pH, concentration, motility, vitality, morphology of spermatozoa, and presence of other cells (immature germ cells and white blood cells).
Semen liquefaction	The process whereby proteolytic enzymes degrade proteins, causing the coagulated semen to liquefy.
Semen viscosity	The description of the relative fluidity of semen. Semen volume: The amount of seminal fluid in an ejaculate.
Semen/Ejaculate	The fluid produced at ejaculation that contains the cells and secretions originating from the testes and sex accessory glands.
Seminal oxidative stress	A process that is initiated by reactive oxygen species (ROS), which include oxygen ions, free radicals and peroxides, and that induces damage to the sperm membrane and DNA. In semen, ROS are typically produced by immature germ cells and white blood cells.
Seminal plasma	The acellular fluid component of semen.
Sertoli cell	A somatic cell type in the seminiferous tubule that mediates the actions of testosterone and follicle stimulating hormone (FSH) in the testis, provides nutrients, cytokines, growth factors, and other proteins to the developing spermatogenic cells, and offers a unique, protective environment for differentiating germ cells because of its dynamic blood-testis-barrier components.
Sertoli cell-only syndrome	A condition in which only Sertoli cells line the seminiferous tubules with an absence of germ cells as seen on testis biopsy. It may also be referred to as germ cell aplasia. Some men with Sertoli cell-only syndrome on biopsy have isolated foci of spermatogenesis in other areas of the testis.
Severe ovarian hyperstimulation syndrome (OHSS)	A systemic response as a result of ovarian stimulation interventions that is characterized by severe abdominal discomfort and/or other symptoms of ascites, hemoconcentration (Hct>45) and/or other serious biochemical abnormalities requiring hospitalization for observation and/or for medical intervention (paracentesis, other).
Sexual orientation	A person's sexual identity, attractions, and behaviours.
Single embryo transfer (SET)	The transfer of one embryo in an ART procedure. Defined as elective (eSET) when more than one embryo of sufficient quality for transfer is available.
Single nucleotide polymorphism (SNP)	Variation at a specific site within the genome, affecting a single nucleotide position and generally involving the substitution of one base (G, A, T or C) for another.
Slow-freezing	A cryopreservation procedure in which the temperature of the cell(s) is lowered in a step-wise fashion, typically using a computer controlled rate, from physiological (or room) temperature to extreme low temperature.
Small for gestational age	A birth weight less than the 10th percentile for gestational age.
Sperm	The male gamete.
Sperm bank	Repository of cryopreserved sperm.
Sperm concentration	The number of spermatozoa per unit volume of semen, generally expressed in millions per one millilitre (mL) of semen.
Sperm DNA fragmentation	The presence of single and double strand DNA breaks in sperm.
Sperm donation	The use of sperm from a donor for reproductive purposes or research.
Sperm donation recipient cycle	A MAR cycle in which a woman receives spermatozoa from a donor.
Sperm isolation	A technique that involves the separation of sperm from seminal plasma, leukocytes and other components before IUI or ART procedures. Different approaches including centrifugation, density gradient centrifugation, microfluidic devices, and "swim-up" may be used to isolate highly motile sperm. Some techniques may also be effective in removing HIV and other infectious particles.
Sperm motility	Moving spermatozoa, usually expressed as a percentage relative to the total number of spermatozoa. There are several types of sperm motility (e.g., non-progressive, progressive, hyperactivated).
Sperm vitality	Live spermatozoa, usually expressed as a percentage relative to the total number of spermatozoa.
Spermatogenic arrest	Failure of germ cells to progress through all stages of spermatogenesis. The arrest of germ cell maturation may occur at any level of sperm production.
Spermatozoon	The male reproductive cell produced in the testis that can fertilize an oocyte. The head carries genetic material, the midpiece provides microtubules that enable normal embryo development in the human and that contains mitochondria to produce energy for movement, and a long, thin tail propels the sperm (Plural: spermatozoa).
Spontaneous abortion/ miscarriage	The spontaneous loss of an intrauterine pregnancy prior to 22 completed weeks of gestation.
Spontaneous reduction/ vanishing sac(s)	The spontaneous disappearance of one or more gestational sacs with or without an embryo or fetus, in a multiple pregnancy documented by ultrasound.
Sterility	A permanent state of infertility.
Stillbirth	A birth following a fetal death after 22 completed weeks of gestation. The death is determined by the fact that, after such separation, the newborn does not breathe or show any other evidence of life, such as heartbeat, umbilical cord pulsation, or definite movement of voluntary muscles. It includes deaths occurring during labor. Early gestation stillbirth is a birth following a fetal death between 22 and 27 completed weeks of gestation. Late gestation stillbirth is a birth following a fetal death after 28 completed weeks of gestation.
Stillbirth rate	Number of stillbirths per 1000 total births (stillbirths plus live births). When calculating stillbirth rate, it must be specified whether both early and late gestation stillbirth are included in the calculation.
Subfertility	An ambiguous term that should not be used.
Syngamy	The process during which the female and male pronuclei fuse.
Teratozoospermia	Reduced percentage of morphologically normal sperm in the ejaculate below the lower reference limit. When reporting results, the reference criteria should be specified.
Term birth	A birth that takes place between 37 and 42 completed weeks of gestation.
Term live birth rate by order of gestation	The number of live births at term divided by the number of total births (stillbirths plus live births) by order of gestation. For the calculation of singleton term live birth rates, only singleton births are included in the numerator and denominator. For the calculation of twin term live birth rates, only twin births are included in the numerator and denominator. For the calculation of triplet+ term live birth rates, only triplet+ births are included in the numerator and denominator.
Testicular sperm aspiration (TESA)	A procedure using a needle placed percutaneously into the testicle with negative pressure on an attached syringe to obtain sperm for use in ICSI.
Testicular sperm extraction (TESE)	A surgical procedure involving one or more testicular biopsies to obtain sperm for use in ICSI.
Thawing	The process of raising the temperature of a slow-frozen cell or cells from the storage temperature to room/physiological temperature.
Third party MAR cycle	A MAR cycle in which reproduction is intended using at least one gamete or embryo originating from a donor. It also includes gestational surrogacy cycles.
Time to pregnancy (TTP)	The time taken to establish a pregnancy, measured in months or in number of menstrual cycles from initiation of trying to become pregnant, or from the start of MAR treatment.
Time-lapse imaging	The recording at regular intervals of image sequences of gametes, zygotes, cleavage-stage embryos, or blastocysts during culture.
Total delivery rate with at least one live birth per aspiration/initiated cycle	The total number of deliveries with at least one live birth resulting from one initiated or aspirated ART cycle, including all cycles in which fresh and/or frozen embryos are transferred, including more than one delivery from one initiated or aspirated cycle if that occurs, until all embryos are used. Notes: The delivery of a singleton, twin, or other multiple pregnancy is MAR/ART registered as one delivery. In the absence of complete data, the total delivery rate is often estimated.
Total fertility rate (TFR)	The average number of live births per woman. It may be determined in retrospect, observed data (Cohort Total Fertility Rate, CTFR) or an estimated average number (Period Total Fertility Rate, PTFR).
Total sperm count	The calculated total number of sperm in the ejaculate (semen volume multiplied by the sperm concentration determined from an aliquot of semen).
Transgender	A term that refers to persons whose gender identities and/or gender expressions are not what is typical for the sex to which they were assigned at birth. Transgender men or women are named according to their gender identity.
Trichotomous cytokinesis	An abnormal cell division, typically during mitosis, where a single cytokinesis event divides a cell into three daughter cells rather than the expected two.
Trisomy	An abnormal chromosomal status characterized by the presence of three homologous chromosomes rather than the normal two. When trisomy is present in all cells in an embryo, most trisomies are not compatible with successful embryonic development and/or establishment of a viable pregnancy.
Trophectoderm	Cells forming the outer layer of a blastocyst that have the potential to develop into the placenta and amniotic membranes.
Tubal pathology	Tubal abnormality resulting in dysfunction of the Fallopian tube, including partial or total obstruction of one or both tubes (proximally, distally or combined), hydrosalpinx and/or peri-tubal and /or peri-ovarian adhesions affecting the normal ovum pick-up function. It usually occurs after pelvic inflammatory disease or pelvic surgery.
Unexplained infertility	Infertility with apparently normal ovarian function, fallopian tubes, uterus, cervix, and pelvis; apparently normal testicular function, genito-urinary anatomy and a normal ejaculate; and adequate exposure to the possibility of pregnancy. The potential for this diagnosis is dependent upon the methodologies used and/or those methodologies available.
Unisomy	A situation where only a single copy of one type of chromosome is present, e.g., the X chromosome in male cells.
Varicocele	Enlarged scrotal veins in the testicular pampiniform plexus. Varicoceles may be associated with infertility, testis atrophy or pain.
Varicocelectomy	Procedure to occlude and/or remove a portion of the internal spermatic veins to prevent reflux of blood toward the testis and the enlargement of the scrotal veins (varicocele).
Vasectomy	Procedure to occlude the vas deferens, typically done for male contraception.
Very low birth weight	Birth weight less than 1500g.
Vitrification	An ultra-rapid cryopreservation procedure that prevents ice formation within a cell whose aqueous phase is converted to a glass-like solid as the temperature drops from physiological to extreme low.
Vitrified-warmed embryo transfer cycle (VET)	An ART procedure in which cycle monitoring is carried out with the intention of transferring one or more vitrified-warmed embryo(s). Note: A VET cycle is initiated when specific medication is provided or cycle monitoring is started in the woman with the intention to treat.
Vitrified-warmed oocyte cycle	An ART procedure in which cycle monitoring is carried out with the intention of transferring one or more embryos resulting from vitrified-warmed oocytes.
Voluntary childlessness	A condition in which a person does not wish to have a child and does not have any biologically, legally or societally related children.
Warming	The process of raising the temperature of a vitrified cell or cells from the storage temperature to room/physiological temperature.
Whole genome amplification (WGA)	Any of a number of distinct methods that aim to amplify all the DNA in a sample. Whole genome amplification seeks to amplify the entire genome, unlike standard polymerase chain reaction (PCR), which targets one or more defined loci for amplification.
Y-chromosome microdeletions	Missing segments of the genetic material on the long arm of the Y-chromosome that encode genes required for normal spermatogenesis.
Zona pellucida	The glycoprotein coat surrounding the oocyte and the embryo until the time of hatching.
Zygote	A single cell resulting from fertilization of a mature oocyte by a spermatozoon and before completion of the first mitotic division.
Zygote intrafallopian transfer (ZIFT)	A procedure in which (a) zygote(s) is/are transferred into the Fallopian tube.

RESULTS

This fourth edition of the International Glossary on Infertility and Fertility Care contains 348 terms and their definitions which are listed in alphabetical order. Between the 3 rd and the current edition, numerous terms were modified to reflect current knowledge and use of language; 14 terms were deleted and 79 new terms were incorporated.

DISCUSSION

This fourth edition of the International Glossary on Infertility and Fertility Care highlights and simultaneously addresses the continuing need for precise, inclusive, and globally agreed terminology in a rapidly evolving field. The definitions presented here were developed by consensus through multiple rounds of written feedback, virtual and in-person meetings, and open discussion, in a process that was designed to balance scientific rigor with inclusivity. In this way, the glossary reflects both the most current knowledge in reproductive science and the diversity of cultural and social contexts in which these terms will be applied.

Advances in reproductive science and the continuous integration of new technologies into clinical practice require ongoing, systematic, and objective evaluation. This encompasses broader societal changes including the growing demands for family building among gender-diverse individuals. Collectively, such evaluation often depends on the analysis of large datasets, which only achieve their full value when built upon standardized definitions.

This glossary addresses these developments by revising existing terms and introducing new ones with careful attention to global inclusivity and diversity. Furthermore, by harmonizing language across regions and disciplines, this glossary facilitates international data collection and interpretation, as well as scientific exchange. We anticipate that this revised glossary will continue to serve as a global reference, strengthen international dialogue, and contribute to infertility and its interventions being monitored and reported in a standardized way, practiced with scientific rigor, and provided with cultural sensitivity and respect for diversity. It is our hope that it will also inform policy making as well as reproductive health education and health literacy among the public and patients who need to make reproductive decisions.

DATA AVAILABILITY

The data underlying this article are available in the article.

AUTHORS’ ROLES

All authors participated in the study design, execution, analysis, manuscript drafting, and critical discussion.

FUNDING

Neither ICMART, responsible for conducting this project, nor any of the participants received specific financial support for their activities in this project. Ferring provided ICMART with a fixed amount to cover venue costs and a one-day hotel accommodation for participants attending the in-person meeting held prior to the ESHRE Congress in June 2025.

Acknowledgements

The authors wish to acknowledge Ferring for its financial contribution to a one-day in-person meeting prior to ESHRE, 2025.

Conflict of interest

Disclosures were provided by all authors, and none reported any conflict of interest related to this manuscript.

REFERENCES

Fauser BC, Adamson GD, Boivin J, Chambers GM, de Geyter C, Dyer S, Inhorn MC, Schmidt L, Serour GI, Tarlatzis B, Zegers-Hochschild F. Declining global fertility rates and the implications for family planning and family building: an IFFS consensus document based on a narrative review of the literature. Hum Reprod Update 2024;30:153–73.
Starrs AM, Ezeh AC, Barker G, Basu A, Bertrand JT, Blum R, Coll-Seck AM, Grover A, Laski L, Roa M, Sathar ZA. Accelerate progress - sexual and reproductive health and rights for all: report of the Guttmacher-Lancet Commission. Lancet 2018;391:2642–92.
Zegers-Hochschild F, Nygren KG, Adamson GD, de Mouzon J, Lancaster P, Mansour R, Sullivan E. The International Committee Monitoring Assisted Reproductive Technology (ICMART) glossary on ART Terminology. Hum Reprod 2006;21:1968–70.
Zegers-Hochschild F, Nygren KG, Adamson GD, de Mouzon J, Lancaster P, Mansour R, Sullivan E. The International Committee Monitoring Assisted Reproductive Technology (ICMART) glossary on ART Terminology. Fertil Steril 2006;86:16–9.
Zegers-Hochschild F, Adamson GD, de Mouzon J, Ishihara O, Mansour R, Nygren K, Sullivan E, Vanderpoel S, World Health Organization. International Committee for Monitoring Assisted Reproductive Technology (ICMART) and the World Health Organization (WHO) revised glossary on ART terminology, 2009. Hum Reprod 2009;24:2683–7.
Zegers-Hochschild F, Adamson GD, de Mouzon J, Ishihara O, Mansour R, Nygren K, Sullivan E, Vanderpoel S, World Health Organization. International Committee for Monitoring Assisted Reproductive Technology (ICMART) and the World Health Organization (WHO) revised glossary of ART terminology, 2009. Fertil Steril 2009;92:1520–4.
Zegers-Hochschild F, Adamson GD, Dyer S, Racowsky C, de Mouzon J, Sokol R, Rienzi L, Sunde A, Schmidt L, Cooke ID, et al. The international glossary on infertility and fertility care, 2017. Hum Reprod 2017;32:1786–801.
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World Health Organization. WHO fact sheet on infertility. Available at: https://www.who.int/news-room/fact-sheets/detail/infertility. 6 November 2025, date last accessed.

Practice Documents

ASRM Practice Documents have been developed to assist physicians with clinical decisions regarding the care of their patients.

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What diagnosis codes should providers submit to insurance carriers while trying to evaluate fertility issues? View the Answer

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Initial Visit for Infertility With No Mandated Coverage

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Monitoring E&M

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How soon can you bill as a new infertility patient? View the Answer

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What is the appropriate ICD-10 code for recurrent implantation failure? View the Answer

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The Z31.41 is or is not the correct code to use for diagnostic testing of an infertile couple? And If so can if be used as the primary and only code? View the Answer

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If a patient comes in only for a blood draw (venipuncture) and is seen only by the lab technician (not an MD, PA, or NP), may we bill for a (minimal) office visit? View the Answer

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