(controlled ovarian stimulation) n. stimulation of the ovary to produce more follicles with oocytes. Usually induced by gonadotrophin preparations (e.g. *human menopausal gonadotrophin, *human chorionic gonadotrophin), it is performed in *in vitro fertilization and other procedures of assisted conception in order to improve the pregnancy rates. See also ovarian hyperstimulation syndrome.
(hCG) a hormone, similar to the pituitary *gonadotrophins, that is produced by the placenta during pregnancy. hCG maintains the secretion of *progesterone by the corpus luteum of the ovary, the secretion of pituitary gonadotrophins being blocked during pregnancy. Large amounts are excreted in the urine, and this is used as the basis for most *pregnancy tests. Serum hCG monitoring is used for tracking early pregnancy and detecting *ectopic pregnancies (in which the level will not double over a 48-hour period, as it does with normal pregnancies). The level of hCG in the serum is also one of the indicators used in *prenatal screening tests: levels are higher in pregnancies affected by Down’s syndrome in comparison with normal pregnancies (see also papp-a; triple test). Levels of hCG are very high in *gestational trophoblastic neoplasia. Some malignant tumours (e.g. malignant teratoma, choriocarcinoma, endodermal sinus tumour) secrete hCG, which can be used as a *tumour marker. A preparation of hCG is given by injection to treat fertility problems due to ovulation disorders and to induce *superovulation in in vitro fertilization.... human chorionic gonadotrophin
(IVF) fertilization of an ovum outside the body, the resultant *zygote being incubated to the *blastocyst stage and then implanted in the uterus. The technique, pioneered in Britain, resulted in 1978 in the birth of the first test-tube baby. IVF may be undertaken when a woman has blocked Fallopian tubes, unexplained infertility, endometriosis, or ovulation disorders; it is also carried out for purposes of surrogacy and egg donation. The mother-to-be is given hormone therapy causing a number of ova to mature at the same time (see superovulation). Several of them are then removed from the ovary through a laparoscope. The ova are mixed with spermatozoa and incubated in a culture medium until the blastocyst is formed. The blastocyst is then implanted in the mother’s uterus and the pregnancy proceeds normally. IVF is regulated by the *Human Fertilisation and Embryology Act 1990 via the Human Fertilisation and Embryology Authority.... in vitro fertilization
a potentially life-threatening condition classically associated with ovarian stimulation using gonadotrophins in assisted conception procedures, such as in vitro fertilization (see superovulation). It is characterized by gross enlargement of the ovaries resulting in pain, bloating, nausea, vomiting, *haemoconcentration, and *ascites. The most severe cases require intensive care due to the high risk of thromboembolism and acute respiratory distress.... ovarian hyperstimulation syndrome
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