The relationship of smoking and ectopic pregnancy.

A case-control study, using data abstracted between 1983 and 1987 from a large perinatal registry, was conducted to explore the relationship between smoking and ectopic pregnancy. Women with ectopic pregnancy (n = 634) seen at University of Illinois Perinatal Network Hospitals were compared to women who were delivered of a single live-born infant (n = 4287). Adjusted for age and race, women who reported smoking during pregnancy had a greater than twofold risk of ectopic pregnancy (Odds Ratio = 2.5, 95% confidence interval = 1.9, 3.2) compared to women who never smoked. The estimated relative risk rose from 1.4 (95% CI = 0.8, 2.5) for a woman smoking fewer than 10 cigarettes a day to 5.0 (95% CI = 2.9, 8.7) at one and a half or more packs of cigarettes per day (p-value for trend less than 0.001). Although further basic and epidemiologic research is necessary, the observed dose-response relation strengthens the argument that smoking may be a causal factor in the development of ectopic pregnancy.