Objective. To assess the risk of ectopic pregnancy by the number of previous induced abortions.
Design. Prospective cohort study.
Methods. Three thousand seven hundred and fifty-four women, 39 years old or younger, living permanently in one Norwegian county, who had had at least one induced abortion between January 1, 1987 and December 31, 1992, at the University Hospital of Trondheim, Norway were followed prospectively for histologically verified ectopic pregnancies until December 31, 1993. Exposure time was measured from the most recent induced abortion (index abortion) until the ectopic pregnancy, closure date, or the subject's 40th birthday. Statistical analyses were done in SAS applying survival analyses and poisson regression.
Results. During the follow-up period of 164,167 women-months, we observed 24 ectopic pregnancies in 3,754 women. The adjusted incidence density ratio (alDR) for women who had had two or more induced abortions was 1.2 (95% CI: 0.5-3.1) in comparison with the reference group of women who had had one induced abortion. Measuring exposure as increasing number of consecutive induced abortions, no dose-response to ectopic pregnancy was found between two consecutive (alDR 0.9) and three or more consecutive abortions (alDR 1.1) in comparison with the reference group.
Conclusion. In our setting, no excess risk of ectopic pregnancy was associated with multiple previous induced abortions compared with one previous induced abortion.