A moral compulsion for ethical action, sometimes usefully distinguished from a duty by its derivation from example or external enforcement. According to this distinction, obligations are derived chiefly from the considerations of teleological ethics and utilitarian ethics, with duties derived from considerations of deontological ethics.

Infrequent menstrual periods. By convention, a menstrual cycle that is consistently longer than 35 days. Oligomenorrhea always reflects irregularity of hormonal events coming from the ovaries.

Strictly, oligozoospermia, meaning a reduced number of sperm cells (spermatozoa) in the ejaculate (compared with azoospermia, which means no sperm in the ejaculate). More generally, a decrease in normal, motile sperm, and more or less encompassing laborious terms such as 'asthenozoospermia' (weak motility) and 'teratozoospermia' (abnormal sperm), and even more laborious ones, such as 'oligoasthenoteratozoospermia', which do not reward the effort of concocting them.

The form of the ovum, or egg, which is undergoing a halving of the number of chromosomes through the process of meiosis;

The multiplication (by the process of mitosis) of ova, or eggs, in the ovaries of the fetus.

The earliest recognisable form of the ovum, or egg; present only in the ovaries of fetuses. Multiplies by the process of mitosis before developing into oocytes by the process of meiosis. The male equivalent (the spermatogonium) normally persists in the testicles till old age. Plural, oogonia.

A new term for the normal cessation of female fertility up to 10 years before the menopause, being apparent in some women after the age of 33 and most women by 45. Different from the perimenopause, which occurs as egg numbers fall far enough to cause shortening of the menstrual cycle, particularly the follicular phase, and accompanied by elevation of serum FSH when measured during menstruation. If pregnancies are attempted through the oopausal transition, a woman who has had no prior reproductive disturbance will typically experience recurrent miscarriages before developing otherwise unexplained infertility, manifesting in the IVF lab sequentially with unexplained implantation failure of apparently satisfactory embryos, then, in turn, a decreased rate of forming blastocysts, defective cleavage, and then failure of fertilisation. There is no known method of overcoming its effects short of egg donation, except for some hope that the procedure of cytoplasmic transfer might be helpful.

Ovum pick-up.

An operation to move an undescended testis into the scrotum, so that it has more chance of developing normally and producing sperm cells (spermatozoa).

The GnRH-antagonist ganirelix made by Organon. Called Antagon in the US.

I don't need to tell you what this is, you can find out for yourself!

An abnormal condition of the bones, which are weakened by a loss of calcium. Deficient estrogen, such as after the menopause or after primary ovarian failure (premature menopause), eventually causes osteoporosis, with a tendency to bone fractures, especially of the wrist, the thigh and the backbone.

The equivalent of the menstrual cycle in the ovary, comprising the follicular phase and the luteal phase. Thus the ordered sequence of timely development of tertiary follicles to a (usually) single dominant follicle or Graafian follicle, characterised by increasing production of the estrogen estradiol), through ovulation, when estradiol falls and progesterone starts to rise, followed by the development and then decline of the corpus luteum, with the further production of progesterone. Because estradiol and progesterone control the growth and development of the endometrium in the uterus, the ovarian cycle determines the menstrual cycle (normally lasting from 24 to 35 days in length, and with a typical duration of about 28 days) and also the cycle of the normal female hypothalamus and pituitary gland.

(OHSS) A complication of ovulation induction with, usually, follicle stimulating hormone, especially in cycles of superovulation for assisted conception, when it is intended to retrieve more than one egg. The ovaries become large, they can be painful, and there is excessive fluid released into the abdomen (the peritoneal cavity). Either removing this fluid or the occurrence of vomiting can cause dehydration, thickening of the blood and, occasionally, a serious thrombosis, such as a stroke. Death has been reported. Moderate to severe OHSS is treated in hospital, with administration of fluid intravenously, sometimes including albumin.

The frequent estimation of serum estradiol (or perhaps estimating the cervical score) and performance of transvaginal ultrasound to estimate how close a woman is to ovulation.

An ectopic pregnancy located in the substance of the ovary, presumably because an egg (an oocyte has been fertilised while still in a follicle).

The place of ovariectomy in the management of endometriosis and incapacitating premenstrual tension. Synonym: oophorectomy.

The female organ that produces eggs, or oocytes. Located on each side of the uterus, to which the ovaries are functionally connected by way of the fallopian tubes (or oviducts).

Recombinant human chorionic gonadotropin made by Serono. Called Ovitrelle in Europe.

Another name for fallopian tube (derived from its function of conducting, or transporting, the ovum).

Natural process by which a mature follicle in the ovary opens to release the secondary oocyte, or egg, enclosed in a sticky blob of mucus-like material, the cumulus mass.

The use of drugs to stimulate the development of follicles in the ovaries to undergo ovulation, such as clomiphene, various preparations containing follicle stimulating hormone (FSH), and human chorionic gonadotropin (hCG). The two main situations for it are: in the treatment of infertility due to anovulation typically when there is oligomenorrhea or amenorrhea; and for superovulation in assisted conception (e.g. in vitro fertilisation and gamete intrafallopian transfer)

A mild pain that precedes ovulation by about 12 hours, felt in the left or right side, but not by everyone or in every ovarian cycle. A good indication of ovulation if it is felt. Can be exaggerated in endometriosis and in so-called pelvic congestion. The time from ovulation pain until the onset of menstruation (ignoring for this purpose any premenstrual spotting) is a good measure of the length of the luteal phase. Should not be treated with NSAIDs such as Advil or Nurofen if you are trying to get pregnant, because these analgesics have been linked to the so-called luteinised unruptured follicle syndrome, or LUF.

Heavy but generally regular bleeding caused either by pathology in the uterus, such as fibroids, or by a generalised bleeding disorder, such as thrombocytopenia (a low platelet count), von Willebrand's disease (can run in families), or treatment with anticoagulant drugs. The formal term for it is menorrhagia.

The female germ cell, or egg, from the earliest stage (the oogonium in the fetus), through its release from the follicle (ovulation), and (to professional embryologists) through fertilisation up to and sometimes beyond the stage of implantation. Plural: ova.