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.





A membrane-bound structure covering the anterior of the sperm head that contains enzymes necessary to penetrate the zona pellucida of the oocyte.


A form of endometriosis marked by the presence of endometrium-like epithelium and stroma outside the endometrium in the myometrium.


Bands of fibrous scar tissue that may bind the abdominal and pelvic organs, including the intestines and peritoneum, to each other. They can be dense and thick or filmy and thin.

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.


Clumping of spermatozoa in the ejaculate.


The medical practice dealing with the health of the male reproductive system.


An abnormal number of chromosomes in a cell. The majority of embryos with aneuploidies are not compatible with life.

Anti-sperm antibodies

Antibodies that recognize and bind to antigens on the surface of the spermatozoon.


Lack of external ejaculation.

Assisted hatching

An ART procedure 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 include the in vitro handling of both human oocytes and sperm or of embryos for the purpose of reproduction. This includes, but is not limited to, IVF and embryo transfer ET, intracytoplasmic sperm injection ICSI, embryo biopsy, preimplantation genetic testing PGT, assisted hatching, gamete intrafallopian transfer GIFT, zygote intrafallopian transfer, gamete and embryo cryopreservation, semen, oocyte and embryo donation, and gestational carrier cycles. Thus, ART does not, and ART-only registries do not, include assisted insemination using sperm from either a woman's partner or a sperm donor. (See broader term, medically assisted reproduction, MAR.)


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.


Reduced percentage of motile sperm in the ejaculate below the lower reference limit. When reporting results, the reference criteria should be specified.


The absence of spermatozoa in the ejaculate.



The presence of two nuclei in a blastomere (cell).

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 gestational age, irrespective of whether it is a live birth or stillbirth, or, if gestational age is unknown, a birth weight more than 500 grams. A single birth refers to an individual newborn; and a delivery of multiple births, such as a twin delivery, would be registered as two births.


Fluid-filled central region of the blastocyst.


The stage of preimplantation embryo development that occurs around day 5–6 after insemination or ICSI. The blastocyst contains a fluid filled central cavity (blastocoele), an outer layer of cells (trophectoderm) and an inner group of cells (inner cell mass).


A cell in a cleavage stage embryo.

Blastomere symmetry

The extent to which all blastomeres are even in size and shape.

Bleeding after oocyte aspiration

Significant bleeding, internal or external, after oocyte aspiration retrieval requiring hospitalization for blood transfusion, surgical intervention, clinical observation or other medical procedure.


Canceled ART cycle

An ART cycle in which ovarian stimulation or monitoring has been initiated 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.


A condition in which a person, voluntarily or involuntarily, is not a legal or societally-recognized parent to a child, or has had all children die.


Presence in a single individual of two or more cell lines, each derived from different individuals.

Cleavage stage embryos

Embryos beginning with the 2-cell stage and up to, but not including, the morula stage.

Clinical fertility

The capacity to establish a clinical pregnancy.

Clinical pregnancy

A pregnancy diagnosed by ultrasonographic visualization of one or more gestational sacs or definitive clinical signs of pregnancy. In addition to intra-uterine 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 heart beat

A pregnancy diagnosed by ultrasonographic or clinical documentation of at least one fetus with a discernible heartbeat.

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.


The process during which tight junctions form between juxtaposed blastomeres resulting in a solid mass of cells with indistinguishable cell membranes.

Complex aneuploidies

Two or more aneuploidies involving different chromosomes in the embryo. When autosomes are involved, this condition is not compatible with human life.

Congenital anomalies

Structural or functional disorders that occur during intra-uterine 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 rate

The number of births exhibiting signs of congenital anomalies per 10,000 births. The time of identification should have been reported.

Congenital bilateral absence of the vasa deferentia (CBAVD)

The absence, at birth, of both duct systems (vas deferentia) that connect the testes to the urethra and may be associated with cystic fibrosis transmembrane conductance regulator (CTFR) gene mutation. Although the testes usually develop and function normally, men present with azoospermia.

Conventional in vitro insemination

The co-incubation of oocytes with sperm in vitro with the goal of resulting in extracorporeal fertilization.

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 or persons legally reside.


The process of slow freezing or vitrification to preserve biological material (e.g. gametes, zygotes, cleavage-stage embryos, blastocysts or gonadal tissue) at extreme low temperature.


Testis not in scrotal position within the neonatal period and, up to but not limited to, 1 year post birth. If the testis has not descended into the scrotum, this condition can cause primary testicular failure and increased risk of testicular cancer development.

Cumulative delivery rate per aspiration/initiated cycle with at least one live birth

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 surrounding the oocyte.

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 transfer

A procedure that can be performed at different stages of an oocyte's development to add to or replace various amounts of cytoplasm from a donor egg.


Decreased spermatogenesis

A histological finding in which spermatogenesis is present with few cells in the seminiferous tubules, resulting in a decreased number or absence of sperm in the ejaculate.

Delayed ejaculation

A condition in which it takes a man an extended period of time to reach orgasm and ejaculation.

Delayed embryo transfer

A procedure in which embryo transfer is not performed within the time frame of the oocyte aspiration cycle but at a later time


The complete expulsion or extraction from a woman of one or more fetuses, after at least 22 completed weeks of gestational age, 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.

Delivery rate after fertility treatment per patient

The number of deliveries with at least one live birth or stillbirth, expressed per 100 patients, after a specified time and following all treatments.

Delivery with multiple births after fertility treatments

A single delivery with more than one newborn, following all fertility treatments.

Diandric oocytes

An oocyte with an extra set of haploid chromosomes of paternal origin.

Digynic oocytes

An oocyte with an extra set of haploid chromosomes of maternal origin.

Diminished ovarian reserve

A term generally used to indicate a reduced number and/or reduced quality of oocytes, such that the ability to reproduce is decreased. (See ovarian reserve.)


The condition in which a cell has two haploid sets of chromosomes. Each chromosome in one set is paired with its counterpart in the other set. A diploid embryo has 22 pairs of autosomes and two sex chromosomes, the normal condition.


The normal number of chromosomes characterized by 22 pairs of autosomal chromosomes and one pair of sex chromosomes (XX or XY). The chromosome number in human cells is normally 46.

Donor insemination

The process of placing laboratory processed sperm or semen from a man into the reproductive tract of a woman who is not his intimate sexual partner, for the purpose of initiating a pregnancy.

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.