The "upper" layer of the embryo as the inner cell mass forms a circular disk two cells thick, giving rise with further embryonic development to the skin, brain and spinal cord. Synonym: epiblast.

A pregnancy implanted in an abnormal location, such as the fallopian tube (see tubal pregnancy), the cervix (see cervical pregnancy), the ovary (see ovarian pregnancy) or the peritoneal cavity (see abdominal pregnancy).

The percentage of ectopic pregnancies among total clinical pregnancies (excluding "biochemical pregnancy"). Until a generation ago, the rate was about 0.3 percent, and this can be regarded as the incidence in normal women. The rate is increased with abnormalities of the fallopian tubes, assisted conception, and other circumstances, so that nowadays ectopic pregnancies account for about 2 percent of pregnancies in western societies.

Fine passages in the rete testis conducting sperm cells (spermatozoa) from the tubules of the testis to the epididymis.

General term for oocyte.

A form of collaborative reproduction comparable in some ways to sperm donation (see donor insemination), but different in that eggs for donation are much harder to obtain physically than ejaculated sperm are; generally the egg donor undergoes all the steps needed for in vitro fertilisation up to the stage of egg retrieval.

Procedure for obtaining eggs (oocytes), involving the passing of a needle into a mature (or preovulatory follicle, either directly at laparoscopy or (more usually) via the vagina guided by transvaginal ultrasound.

The word is used loosely to describe everything from a fertilised egg (or zygote) to a fetus, including the embryo. What nowadays we call the embryo has for long been called the ovum by professional embryologists.

A biopsy, or removal of one or two cells, from an early IVF embryo for preimplantation genetic diagnosis after in vitro fertilisation.

(ET) Procedure by which the embryo is placed in the uterus or into the fallopian tube after in vitro fertilisation.

Literally, pathology of the embryo (or fetus). Can underlie a miscarriage or, if it reflects are more or less permanent state, can cause unexplained infertility.

More than feeling compassion or sympathy "for" another person, empathy puts you in their shoes to feel "with" them or "as one" with them. First used in English in the early twentieth century to translate the German psychoanalytic term Einfühlung, meaning "to feel as one with", though in practice more closely translating the German Mitgefühl, "to feel with" someone.

An awkward adjective that can have contrary meanings in medicine. The word comes from the Greek for experience. On the one hand, empirical medical practice is that which is based only on observation and experiment (praiseworthy); on the other, it can refer to medical practice that's based on very personal experience without taking scientific principles into account (not praiseworthy); at worst it refers to treatment that's chosen on no other basis than: "Let's see if it might work".

A natural or pollutant substance in the environment possibly capable of acting -- alone or in combination with other substances -- as an estrogen or as a blocker of androgens during development of the fetus. Suspected of causing endometriosis and oligospermia in later life.

The study of hormones, including their production, their action and their excretion.

The "lower" layer of the embryo, as the inner cell mass forms a circular disk two cells thick; with further embryonic development it gives rise to the digestive tract and its glands. Synonym: hypoblast.

Diminishment of the endometrium through lack of support by, especially, the hormone estrogen or by the loss, through chronic endometritis and/or injury at curettage under abnormally low estrogen conditions, of subsequent receptiveness to estrogen. Can cause light periods hypomenorrhea or absent periods amenorrhea.

The space inside the uterus lined by the endometrium.

Overgrowth of the endometrium, caused usually by prolonged action of estrogen unopposed by progesterone (i.e. prolonged anovulation), as is the case in, particularly, the polycystic ovary syndrome. Potentially dangerous, because it can turn to cancer of the endometrium. Can be suspected by an echogenic appearance of the endometrium on transvaginal ultrasound and is confirmed by pathological examination of tissue obtained at curettage.

A polyp of the endometrium (lining of the uterus), sometimes without symptoms, sometimes with abnormal bleeding such as intermenstrual bleeding, premenstrual spotting or heavy periods. A cause of infertility (and of failure of assisted conception to result in pregnancy). Diagnosable with transvaginal ultrasound.

An operation performed at hysteroscopy to treat menorrhagia by intentionally producing endometrial atrophy and intrauterine adhesions.

Loose connecting-type ('connective') tissue that lies between glands of the endometrium. Contains stromal cells that eventually respond to progesterone by becoming plump to form a more or less continuous sheet towards the end of the menstrual cycle (the predecidual reaction) or, more completely, with successful implantation and pregnancy (the decidual reaction).

A common condition in which tissue like the lining of the uterus (the endometrium), grows somewhere else, sometimes causing dysmenorrhea, premenstrual spotting, infertility, dyspareunia and ovulatory dysfunctional uterine bleeding.

Inflammation of the endometrium (the lining of the uterus). Can be acute or chronic. Not related to endometriosis

The lining of the uterus, which contains the endometrial glands and the endometrial stroma. Distinct from the myometrium.

Opium-like substances produced naturally in the brain, which give a feeling of well-being. Production of endorphins is stimulated by many natural circumstances, and also by profound exercise (to which people can become "addicted"!). Depressed in premenstrual tension.

The physical, chemical, biological and social milieu in which we live. See also congenital and endocrine disrupter. This environment is sometimes called the external environment, in contrast to an internal environment that might describe the physical and chemical milieu inside the body, around a particular organ, tissue, cell or intracellular organelle.

A protein found in cells and secretions that acts as a catalyst, greatly promoting a chemical transformation for a special purpose. Enzymes are important in every aspect of biology, including the production (and destruction) of hormones.

A finely coiled tubular structure, lying next to each testis in the scrotum, which connects the testis to the vas deferens, and through which sperm cells (or spermatozoa) pass and gain in maturity.

Embryonic stem cells.

Elective single embryo transfer. Choosing to have just one embryo transferred after in vitro fertilisation even though there is more than one embryo that is suitable; the other suitable embryos are frozen and stored. A strategy to increase the chance of taking home a baby by minimising the risk of multiple pregnancy, which carries a higher risk of miscarriage and stillbirths.

The most powerful natural estrogen. Produced by the ovarian follicle and corpus luteum in women, and (to a small extent) by the Sertoli cells in men. Also produced by fat cells (through conversion of testosterone) in older women, especially after the menopause.

A weak estrogen. Increased in pregnancy, especially late pregnancy.

The general name for one of the two principal female sex hormones (the other is progesterone), responsible for stimulating growth of the female reproductive system (the vagina, the cervix, the uterus and the fallopian tubes) and growth of the breasts. The main estrogen is estradiol, produced by: the developing follicle (and to a lesser extent by the corpus luteum) in the ovary; by the trophoblast of the placenta; and by the body's fat tissues (through conversion from male sex hormones, or androgens, in the blood). After the menopause the main estrogen is the weaker one, estrone, largely derived from conversion by the body's fat of the weak androgen androstenedione.

(ERT) The therapeutic use of estrogen to stop the effects of menopause after the ovaries have been removed or have stopped functioning. If the uterus is still present the hormone regimen must include at least 11 days' progestogen usage each month, or there will be a risk of endometrial hyperplasia and hence endometrial cancer.

A weak estrogen, which needs to be converted (in target tissues such as the endometrium) to the strong estrogen estradiol before, as a hormone, it causes an estrogen effect. The main estrogen in blood after the menopause. Formed from estradiol when that hormone in tablet (or oral) forms is absorbed across the intestines. Abbreviated E1.

A set of principles and values that govern behavior to accord with a notion of morality. See especially deontological ethics, teleological ethics and utilitarian ethics, and also see autonomy, beneficence, non-maleficence, justice and suffering. The ethics of assisted reproductive technology, collaborative reproduction, the doctor-patient relationship, informed consent and human embryo research are much debated.

Orally effective form of estradiol that resists being converted to estrone after ingestion. Generic ('no frills') name for Estigyn and Progynon C.

The last stage of development of the blastocyst before it hatches out of the zona pellucida prior to implantation.

The outermost layer of trophoblast, produced by cytotrophoblast where there is direct contact with maternal decidua rather than blood. The EVT cells travel into the decidua, reacting with NK cells and invading maternal blood vessels feeding the placenta, softening the walls and replacing the lining with fetal tissue, a process called "conversion". Also known as interstitial or intermediate trophoblast.

A trisomy with a karyotype of 47,XYY -- i.e. a male with an extra Y-chromosome. Affected men tend to be tall. Surveys of penal institutions have indicated a higher than expected frequency, implying that affected men are at increased risk of being criminals. This assertion is controversial.