Objective: To analyze risk factors for ectopic pregnancy in a population at low risk for the disease.
Methods: Between September 1989 and February 1991 in Milan, we conducted a case-control study on 120 cases of ectopic pregnancy and 209 controls. The control subjects gave birth at term (more than 37 weeks' gestation) to healthy infants on randomly selected days at the same hospitals where the cases had been identified.
Results: The risk of ectopic gestation was about 40% higher in smokers than in controls, and the risk estimates increased with the number of cigarettes smoked per day (chi 2(1) trend 4.21, P = .04) and the duration of smoking (chi 2(1) trend 7.31, P < .01). However, smoking was not associated with the risk of ectopic pregnancy after adjustment for potential confounding factors (including history of pelvic inflammatory disease) in a multivariate analysis (relative risks [RRs] for ten or fewer and more than ten cigarettes per day versus no smoking were 0.8 and 1.1, respectively; chi 2(1) trend 0.10, P = not significant). Infertility problems or difficulty in conception were reported by 32% of the cases and 10% of the controls; the corresponding multivariate RR was 4.7 (95% confidence interval [CI] 2.3-9.5). A history of abdominal surgery was associated with about double the risk of ectopic pregnancy (multivariate RR 2.4, 95% CI 1.4-4.2). Similar estimates were found when the analysis was performed considering various types of surgery separately such as appendectomy, cesarean delivery, and other abdominal surgery. Finally, the risk of ectopic pregnancy was higher in women reporting a history of pelvic inflammatory disease (RR 2.7, 95% CI 0.9-8.7) and increased with the number of sexual partners (chi 2(1) trend 4.51, P = .03).
Conclusions: Problems of infertility or difficulties in conception, history of pelvic inflammatory disease/salpingitis, and abdominal surgery are the main risk factors for ectopic pregnancy in this Italian study. Sexual habits also appear to have some independent effect.