Past use of an intrauterine device and risk of tubal pregnancy.

We assessed risk of tubal pregnancy associated with past use of an intrauterine device (IUD). Cases were 256 members of Group Health Cooperative of Puget Sound who experienced a tubal pregnancy between 1981 and 1986. Controls were 666 female members of the Cooperative at risk of ectopic pregnancy who were similar to cases with respect to age and county of residence, but otherwise selected at random. The presence of antibody to Chlamydia trachomatis was assessed in a sample of 134 cases and 182 controls. Women who had previously used an IUD for 3 or more years were more than twice as likely as women who had never used an IUD to have a tubal pregnancy (adjusted relative risk = 2.5, 95% confidence interval = 1.5-4.3). Among these long-term users of an IUD, risk of tubal pregnancy remained elevated for many years after the device was removed. Also, among long-term users, women known to have more than one IUD insertion were no more likely than women with one known insertion to develop a tubal pregnancy. When we restricted our analyses to women who used only copper-containing devices, the results were nearly identical. We conclude that extended past use of an IUD, including use of a copper device, increases the risk of tubal pregnancy.