Pregnancy loss

Causes and prevention

About half of the miscarriages that occur are caused by genetic abnormalities, which may be hereditary or spontaneous, in the father's sperm or the mother's egg. The other half are caused by a variety of known and unknown factors, including infection (mumps, for instance, in the first trimester increases the risk of miscarriage) and exposure to environmental and work place hazards.

Other factors that may cause miscarriage are hormonal irregularities; uterine abnormalities; radiation; and drugs, whether recreational (including alcohol), over-the-counter or prescription.

Severe malnutrition can cause a miscarriage, as can a higher blood sugar level in women with diabetes. If dietary problems are the culprit, then an improved diet sometimes helps prevent miscarriage. Induced ovulation with fertility drugs sometimes result in miscarriages, as does in vitro fertilisation. Two antenatal tests, amniocentesis and chorionic villi sampling (CVS), are also associated with a slight risk of miscarrying.

To prevent miscarriage, some women are treated with progesterone, a hormone needed for implantation in the uterus. Research is mixed on the effectiveness of this, and researchers believe it should only be done if tests show that the body is producing too little of that hormone in the early weeks of pregnancy.

Repeated miscarriages

Most women who have miscarriages have subsequent normal pregnancies and births. About one per cent of pregnant women have repeated (three or more) miscarriages, usually without a history of any normal births. Some researchers believe that this is an auto-immune disorder.

Starting periods early in puberty, before the age of 11, or late — after 16 — is associated with multiple miscarriages, as are ovaries with many cysts. Women who have repeated miscarriages are four times more likely to have multiple ovarian cysts. Another link to repeated miscarriages is an allergy to the partner's sperm. Some women go on to have normal pregnancies and births after they change partners.