The epidemiology of recurrent pregnancy loss.

In reviewing the epidemiology of recurrent abortion (RAB), we believe it is necessary to consider the epidemiology of spontaneous abortion (SAB) as well, since it is clear that even a single pregnancy loss increases the risk for a subsequent abortion. In addition, any attempt to identify epidemiologic risk factors for SAB or RAB must deal with the fact that at least 50% of SABs are associated with genetic abnormalities. Given that most epidemiologic studies have not distinguished karyotypically abnormal abortuses, risk factors are likely to be underestimated. Nevertheless, there is fair agreement that a variety of factors may increase risk for SAB or RAB, including advanced maternal age, single gene mutations such as PKU or G6PD deficiency, structural abnormalities of the uterus, poorly controlled diabetes, antiphospholipid syndrome, and smoking. More controversial is the role of luteal phase defect or hyperandrogenism, alloimmune factors, genital infections, caffeine or alcohol use, and trace element or chemical exposure from tap water or in the workplace. Besides better designed epidemiologic studies to detect modifiable risk factors for SAB or RAB, there is a clear need for clinical trials of therapy for RAB which meet minimum epidemiologic standards including randomization, double-blinded (when possible), and placebo-controlled (when ethical).