Approximately 1 percent of women experience recurrent miscarriage, which is defined as three consecutive miscarriages of pregnancies conceived with the same partner. Approximately 75 percent of these women report recurrent first trimester losses, and 5 percent report recurrent second trimester losses. After three consecutive miscarriages, an underlying cause can be identified in up to 40 percent of cases. A review by Rutherford and Shillito stresses the need for supportive care of these patients and families, even if a cause cannot be identified.

The most common cause of recurrent miscarriage is polycystic ovary syndrome (see accompanying table). Although any chronic maternal disease is associated with increased risk of repeated miscarriage, poor diabetic control is not significantly associated unless glycosylated hemoglobin (HbA_1c) levels exceed four standard deviations above normal. Chromosomal abnormalities and maternal febrile illnesses are not common causes of recurrent miscarriage. The couples in whom chromosomal abnormalities are identified as causing recurrent pregnancy loss (5 percent) should be referred for genetic counseling and offered support from the primary care health team.

Recurrent early miscarriage is one of the common obstetric manifestations of anti-phospholipid antibody syndrome. Other features include intrauterine fetal death and deliveries before 34 weeks' gestation associated with pregnancy-induced hypertension or intrauterine growth retardation. Mothers may also have livedo reticularis, arterial or venous thrombosis, or neurologic conditions such as migraine, epilepsy, chorea, or transient ischemic attacks. Laboratory confirmation includes IgG anticardiolipin antibodies, lupus anticoagulant, and thrombocytopenia. Because the pregnancy loss is believed to be thrombotic, treatment involves a combination of low-dose aspirin and prophylactic heparin.

Congenital structural abnormalities such as bicornuate uterus and septate uterus are believed to cause about 5 percent of recurrent miscarriages, but the results of corrective surgery are difficult to evaluate. Structural abnormalities causing cervical incompetence are also believed to cause 5 percent of cases. The cervix may have been damaged by previous deliveries or surgeries. Cervical suture at the end of the first trimester is recommended.

In patients with idiopathic recurrent miscarriage, studies of the use of progesterones, immunotherapy, and human chorionic gonadotropin during subsequent pregnancies have shown little or no benefit. Some authors suggest using low-dose aspirin because it has proven benefit in thrombophilia and immune disorders. It is inexpensive and has few side effects and no significant fetal effects.

All patients with recurrent miscarriage should be questioned about beliefs and fears. Appropriate advice and reassurance should be given, because lifestyle factors, including lifting, exercise, travel, and sexual intercourse, are no longer believed to contribute to recurrent miscarriage. Investigations should be individualized to diagnose the etiology of the pregnancy loss. Women attempting subsequent pregnancies should be offered preconception advice about rubella immunization, folic acid supplementation, and general health.