The International Glossary on Infertility and Fertility Care

The following glossary was developed in 2017 by a global panel of more than 100 multidisciplinary experts, professional organisations, and patient representatives to provide consensus agreement on 283 items and definitions. Published in Fertility and Sterility (FNS) and Human Reproduction (HR).

A printable version of the 2017 Glossary and more information on the methodology, and a list of previous compiled glossaries can be found here.




Natural cycle ART

An ART procedure in which one or more oocytes are collected from the ovaries during a menstrual cycle without the use of any pharmacological compound.


The description of an ejaculate in which no live spermatozoa can be found.

Neonatal death/mortality

Death of a live born baby within 28 days of birth. This can be sub-divided into a) early, if death occurs in the first 7 days after birth; and b) 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.

Non-obstructive azoospermia

Absence of spermatozoa in the ejaculate due to lack of production of mature spermatozoa.

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.


A term for low semen volume now replaced by hypospermia to avoid confusion with oligozoospermia.


Low concentration of spermatozoa in the ejaculate below the lower reference limit. When reporting results, the reference criteria should be specified.


The female gamete (egg).

Oocyte aspiration

Ovarian follicular aspiration performed with the aim of retrieving oocytes.

Oocyte bank

Repository of cryopreserved oocytes stored for future use.

Oocyte cryopreservation

The freezing or vitrification of oocytes for future use.

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 maturation triggering

An intervention intended to induce an oocyte in vitro or in vivo to resume meiosis to reach maturity (i.e. to reach metaphase II).

Oocyte recipient cycle

An ART cycle in which a woman receives oocytes from a donor, or her partner if in a same sex relationship, to be used for reproductive purposes.


The cytoplasmic membrane enclosing the oocyte.


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, hemodynamic and metabolic complications.

Ovarian reserve

A term generally used to indicate the number and/or quality of oocytes, reflecting the ability to reproduce. Ovarian reserve can be assessed by any of several means. They include: female age; number of antral follicles on ultrasound; anti-Mullerian hormone levels; follicle stimulating hormone and estradiol levels; clomiphene citrate challenge test; response to gonadotropin stimulation, and oocyte and/or embryo assessment during an ART procedure, based on number, morphology or genetic assessment of the oocytes and/or embryos.

Ovarian stimulation (OS)

Pharmacological treatment with the intention of inducing 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 slow-freezing or vitrification of tissue surgically excised from the ovary with the intention of preserving reproductive capacity.

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.


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 normal ovulatory cycles.


Parthenogenetic activation

The process by which an oocyte is activated to undergo development in the absence of fertilization.


The product of an oocyte that has undergone activation in the absence of the paternal genome, with (induced) or without (spontaneous) a purposeful intervention.

Percutaneous epididymal sperm aspiration (PESA)

A surgical 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 (at 22 completed weeks of gestational age and later), during childbirth, or up to seven completed days after birth.

Perinatal mortality rate

The number of perinatal deaths per 1000 total births (stillbirths plus live births).

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 at 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.)

Pituitary down-regulation

A medical or 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 comprising single chromatids (1c).

Polycystic ovary (PCO)

An ovary with at least 12 follicles measuring 2–9 mm in diameter in at least one ovary (Rotterdam criteria). PCO may be present in women with PCOS, but also in women with normal ovulatory function and normal fertility.

Polycystic ovary 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 hyperandrogenemia); (3) Polycystic ovaries, as assessed by ultrasound scan with more than 24 total antral follicles (2–9 mm in size) in both ovaries.


The condition in which a cell has more than two haploid sets of chromosomes: e.g. a triploid embryo has three sets of chromosomes and a tetraploid embryo has four sets. Polyploidy in a human embryo is not compatible with life.


The process by which an oocyte is penetrated by more than one spermatozoon.

Poor ovarian responder (POR) in assisted reproductive technology

A woman treated with ovarian stimulation for ART, in which at least two of the following features are present: (1) Advanced maternal age (R40 years); (2) A previous poor ovarian response (%3 oocytes with a conventional stimulation protocol aimed at obtaining more than three oocytes); and, (3) An abnormal ovarian reserve test (i.e. antral follicle count 5–7 follicles or anti-Mullerian hormone 0.5–1.1 ng/ml (Bologna criteria); or other reference values obtained from a standardized reference population.)

Poor ovarian response (POR) to ovarian stimulation

A condition in which fewer than four follicles and/or oocytes are developed/obtained following ovarian stimulation with the intention of obtaining more follicles and oocytes.

Post-implantation embryo

An embryo at a stage of development beyond attachment to the endometrium to eight completed weeks after fertilization, which is equivalent to 10 weeks of gestational age.

Post-term birth

A live birth or stillbirth that takes place after 42 completed weeks of gestational age.

Posthumous reproduction

A process utilizing gametes and/or embryos from a deceased person or persons with the intention of producing offspring.

Pre-implantation embryo

An embryo at a stage of development beginning


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 circulating hCG concentration is compatible with ultrasound visualization of a gestational sac.

Preimplantation genetic diagnosis (PGD) and screening (PGS)

These terms have now been replaced by preimplantation genetic testing PGT. (See term PGT and its definitions.)

Preimplantation genetic testing (PGT)

A test performed to analyze the DNA from oocytes (polar bodies) or embryos (cleavage stage or blastocyst) for HLA-typing or for determining genetic abnormalities. These include: PGT for aneuploidies (PGT-A); PGT for monogenic/single gene defects (PGT-M); and PGT for chromosomal structural rearrangements (PGT-SR).

Premature ejaculation

A condition in which semen is released sooner than desired.

Premature ovarian insufficiency

A condition characterized by hypergonadotropic hypogonadism in women younger than age 40 years (also known as premature or primary ovarian failure). It includes women with premature menopause.

Preterm birth

A birth that takes place after 22 weeks and before 37 completed weeks of gestational age.

Primary childlessness

A condition in which a person has never delivered a live child, or has never been a legal or societallyrecognized parent to a child.

Primary female infertility

A woman who has never been diagnosed with a clinical pregnancy and meets the criteria of being classified as having infertility.

Primary involuntary childlessness

A condition in a person with a child wish, who has never delivered a live child, or has never been a legal or societally-recognized parent to a child. A major cause of primary involuntary childlessness is infertility.

Primary male infertility

A man who has never initiated a clinical pregnancy and meets the criteria of being classified as infertile.

Pronuclei transfer

Transfer of the pronuclei from a patient's zygote to an enucleated donated zygote.


A round structure in the oocyte surrounded by a membrane containing chromatin. Normally, two pronuclei are seen after fertilization, each containing a haploid set of chromosomes, one set from the oocyte and one from the sperm, before zygote formation.