Contraceptive methods and risk of pelvic endometriosis

The relation between contraceptive methods and risk of pelvic endometriosis has been analyzed in a case-control study. Cases were 376 women with laparoscopically or laparotomically confirmed pelvic endometriosis admitted to a network of Obstetrics and Gynecology Clinics in Lombardy, Northern Italy. Controls were 522 women admitted for acute non-gynecological and non-obstetrics conditions to the same hospitals where cases had been identified. A total 153 women (40.3%) out of the 377 cases and 154 (29.7%) out of the 522 controls reported ever oral contraceptive (OC) use: the corresponding relative risk (RR) was 1.6 (95% confidence interval, CI, 1.2-2.2). The risk was restricted to ex-OC users (RR 1.7, 95% CI 1.3-2.4), the estimated RR for current users being 0.9 (95% CI 0.5-1.9). No clear relation emerged with duration, recency and latency of OC use and risk of endometriosis. In comparison with never IUD users, the risk for ever users was 1.3 (95% CI 0.6-2.8), and no clear relation emerged with duration of use. Likewise, no association was observed between barrier method of contraception and risk of endometriosis (RR ever vs never users 0.5, 95% CI 0.3-1.4). The role of selection and other biases should be considered in the interpretation of epidemiological data on the role of OC on the risk of endometriosis.