Risk factors for spontaneous abortion.

A case-control study was conducted to evaluate risk factors for spontaneous abortions. Cases were 94 women with two or more unexplained miscarriages (after exclusion of genetic, endocrine and Müllerian factors) and no term pregnancy, controls were 176 women admitted for normal delivery to the same clinic where cases were identified. Questions were asked about personal characteristics and habits, and gynaecological history. A family history of recurrent miscarriage was more common among women with spontaneous miscarriages than among the controls (13 cases versus 8 controls, relative risk (RR) = 3.2, 95% confidence interval (CI) = 1.3-8.1). Compared to women whose menarche occurred at age 11 or younger, the RRs were 0.8 when menarche occurred at age 12-13 and 0.5 at age 14 or more: this trend in risk was statistically significant. Compared with never smokers, current smokers had about a 40% increased risk of miscarriage and the risk increased with number of cigarettes per day. No association emerged with sociodemographic characteristics (e.g. education, marital status, age of the partner), reproductive history (age at first pregnancy), type of contraceptive used and other general lifestyle habits (e.g. alcohol or coffee consumption).