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.




Iatrogenic testicular failure

Damage to testicular function after radiation, chemotherapy or hormone treatment; or devascularization as a consequence of hernia surgery.

Immature oocyte

An oocyte at prophase of meiosis I, (i.e. an oocyte at the germinal vesicle (GV)-stage.)


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 gestation 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 extracorporeal fertilization of gametes. It includes conventional in vitro insemination and ICSI.

In vitro maturation (IVM)

A sequence of laboratory procedures that enable extracorporeal maturation of immature oocytes into fully mature oocytes that are capable of being fertilized with potential to develop into embryos.

Induced abortion

Intentional loss of an intrauterine pregnancy, through intervention by medical, surgical or unspecified means. (See induced embryo/fetal reduction.)

Induced embryo/fetal reduction

An intervention intended to reduce the number of gestational sacs or embryos/fetuses in a multiple gestation.


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 his/her partner. Fertility interventions may be initiated in less than 1 year based on medical, sexual and reproductive history, age, physical findings and diagnostic testing. Infertility is a disease, which generates disability as an impairment of function.

Infertility counseling

A professional intervention with the intention to mitigate the physical, emotional and psychosocial consequences of infertility.

Initiated medically assisted reproduction cycle (iMAR)

A cycle in which the woman receives specific medication for ovarian stimulation or in which cycle monitoring is carried out with the intention to treat, irrespective of whether or not insemination is performed, follicular aspiration is attempted in an ovarian stimulation cycle or whether egg(s) or embryo(s) are thawed or transferred in a frozen embryo transfer (FET) cycle.

Inner cell mass

A group of cells attached to the polar trophectoderm consisting of embryonic stem cells, which have the potential to develop into cells and tissues in the human body, except the placenta or amniotic membranes.

Intended parent(s)

A couple or person who seek(s) to reproduce with the assistance of a gestational carrier or traditional gestational carrier.

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.

Intracytoplasmic sperm injection (ICSI)

A procedure in which a single spermatozoon is injected into the oocyte cytoplasm.


Laparoscopic ovarian drilling

A surgical method for inducing ovulation in females with anovulatory or oligo-ovulatory polycystic ovarian syndrome, utilizing either laser or electrosurgery

Large for gestational age

A birth weight greater than the 90th centile 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.


A high number of white blood cells in semen above the upper reference limit. When reporting results, the reference criteria should be specified.

Leydig cell

Type of testicular cell located in the interstitial space between the seminiferous tubules, that secretes testosterone.

Live birth

The complete expulsion or extraction from a woman of a product of fertilization, after 22 completed weeks of gestational age; which, after such separation, breathes or shows any other evidence 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 births refer to the individual newborn; for example, 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 cycle attempts. In the case of ART/MAR interventions, they can be initiated cycles, insemination, 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.

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.


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 primarily by male factors encompassing: 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 spindle transfer

Transfer of the maternal spindle (including maternal chromosomes) from a patient's oocyte into a donated oocyte in which the maternal spindle with chromosomes has been removed.

Mature oocyte

An oocyte at metaphase of meiosis II, exhibiting the first polar body and with the ability to become fertilized.

Maturing oocyte

An oocyte that has progressed from prophase I but has not completed telophase I, thus does not exhibit the first polar body.

Medically assisted reproduction (MAR)

Reproduction brought about through various interventions, procedures, surgeries and technologies to treat different forms of fertility impairment and 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 extracted for IVF and/or ICSI.

Micromanipulation in ART

A micro-operative ART procedure performed on sperm, egg or embryo; the most common ART micromanipulation procedures are ICSI, assisted hatching and gamete or embryo biopsy for PGT.

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. In the absence of optical magnification, any surgical procedure to retrieve sperm from the epididymis should also be registered as MESE.

Mild ovarian stimulation for IVF

A protocol in which the ovaries are stimulated with gonadotropins, and/or other pharmacological compounds, with the intention of limiting the number of oocytes following stimulation for IVF.

Missed spontaneous abortion/missed miscarriage

Spontaneous loss of a clinical pregnancy before 22 completed weeks of gestational age, in which the embryo(s) or fetus(es) is/are nonviable and is/are not spontaneously absorbed or expelled from the uterus.

Modified natural cycle

An ART procedure in which one or more oocytes are collected from the ovaries during a spontaneous menstrual cycle. Pharmacological compounds are administered with the sole purpose of blocking the spontaneous LH surge and/or inducing final oocyte maturation.


The absence of one of the two homologous chromosomes in embryos. Autosomal monosomies in embryos are not compatible with life. Embryos with sex chromosome monosomies are rarely compatible with life.


An embryo formed after completion of compaction, typically 4 days after insemination or ICSI.


A state in which there is more than one karyotypically distinct cell population arising from a single embryo.


The presence of more than one nucleus in a cell.

Multiple birth

The complete expulsion or extraction from a woman of more than one fetus, after 22 completed weeks of gestational age, 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.