• case-control study;
  • contraceptive efficacy;
  • copper intrauterine devices;
  • ectopic pregnancy

Objective. To assess the risk of ectopic pregnancy when using copper intrauterine devices relative to non-use of coniraception and female sterilization.

Design. Case-control study.

Material and methods. All cases diagnosed with a histologically verified extrauterine pregnancy and who became spontaneously pregnant in one Norwegian county from January 1, 1987 through to December 31, 1990 were eligible. Non-pregnant control women were chosen at random from the Norwegian Population Registry. Eligible for study were sexually active women, from 20 to 39 years of age, and who defined themselves as fecund. Included in the final analyses were 168 cases and 1,169 controls, who had all been previously pregnant. Statistical methods. Chi square test and unconditional logistic regression.

Results. Compared with non-users of contraception, the adjusted odds ratio (aOR) among current users of copper intrauterine devices was 0.09 (95% confidence intervals (CI); 0.06 0.13). Compared with women who were sterilized, the aOR of having an ectopic pregnancy among current copper IUD users was 1.6 (95% CI; 0.7-3.5).

Conclusion. Relative to non-users of contraception, current copper IUD users had a 91% (95% CI; 87-94%) protection against ectopic pregnancy, while compared with women who had had a tubal sterilization, current copper IUD users had a 60% non-significant increased risk of ectopic pregnancy.