Current use of an intrauterine device and risk of tubal pregnancy

Using data from a population-based, case-control study, we assessed risk of tubal pregnancy associated with use of an intrauterine device (IUD) at the time of conception. Cases were 249 members of Group Health Cooperative of Puget Sound who experienced a tubal pregnancy between 1981 and 1986. Controls were 831 members at risk of ectopic pregnancy who were similar to cases with respect to age and county of residence, but otherwise selected at random. Risk of tubal pregnancy associated with current IUD use was compared separately to that among users of various other (or no) contraceptive methods. Tubal pregnancy was more likely to occur among IUD users than among women using oral contraceptives [relative risk (RR) = 3.8, 95% confidence interval (CI) = 1.5-9.9] or barrier methods (RR = 3.6, 95% CI = 1.6-8.1), or, to a lesser extent, among women who had been surgically sterilized (RR = 1.6, 95% CI = 0.8-3.5). In contrast, IUD users were much less likely to experience a tubal pregnancy (RR = 0.2, 95% CI = 0.1-0.4) than were women who were currently not contracepting. For most women, the decision to use an IUD occurs within the context of choosing among various contraceptive methods. Our results indicate that, for these women, the decision to use an IUD results in increased risk of ectopic pregnancy while the device is in use.