An abnormal conceptus in which the chorionic villi of the placenta have become cystic and swollen, typically because the chorion has not developed in connection with a fetus that has a properly functioning circulation. The placenta looks like a bunch of grapes.

A hydatidiform mole in which there is no embryo or fetus. The size of the uterus is often larger than expected from the date of the last menstrual period, often with a high level of serum hCG; there may be bleeding; and there is a classic abnormal appearance on transvaginal ultrasound. Caused by pregnancy following abnormal fertilisation in which the oocyte is 'empty', that is it loses its pronucleus, and either (1) the male pronucleus from a single fertilising sperm doubles (the karyotype of the mole is then always 46,XX, because 46,YY is immediately lethal) or (2) there are two male pronuclei from two fertilising sperm (in which case the karyotype is either 46,XX or 46,XY). Treatment is by vacuum curettage, but there is a persisting danger of cancer (choriocarcinoma) and specialist medical follow-up is essential.

Abnormal conceptus in which there is coexistence of a hydatidiform mole with a fetus; caused by triploidy. Not as dangerous as a molar pregnancy without a fetus (see hydatidiform mole, complete), but medical follow-up is still necessary.

Measurement of human chorionic gonadotropin in serum: essentially a pregnancy test, but carried out more precisely (quantitatively) than is the case with a yes or no test (which is qualitative). Often carried out serially, to determine if a pregnancy is: thriving (hCG levels double every two or three days in normal early pregnancy; languishing (levels rise more slowly, seen with an ectopic pregnancy and with an inevitable miscarriage); or resolving naturally (levels that are falling). Very high levels are seen with hydatidiform mole. Part of the triple screen used to screen for Down syndrome in early pregnancy.

A state of 69 chromosomes, or three times the haploid number, most commonly caused by fertilisation of the egg with two sperm; the embryo that results can develop as far as a fetus, but is doomed to miscarry. The trophoblast of the placenta often undergoes partial changes of a hydatidiform mole. The noun form for this adjective is triploidy (the state of being triploid).

Curettage in which the contents of the early pregnant uterus are sucked out using a soft plastic catheter. Used in the treatment of miscarriage, in the treatment of hydatidiform mole, and to induce abortion.