Evaluation of induced abortion as a risk factor for ectopic pregnancy. A case-control study.

OBJECTIVE

To assess the risk of ectopic pregnancy after one or more induced abortions.

DESIGN

Population-based case-control study.

METHODS

We studied all women who had a histologically verified ectopic pregnancy in one Norwegian county between January 1, 1987, and December 31, 1990. We identified population-based control sets of women among participants in the second Norwegian fertility study (1988-1989). Gravida women 20-39 years of age, who were not using contraceptives and had become spontaneously pregnant, were eligible for analysis. The final analyses included 174 women with ectopic pregnancy, 115 pregnant control women and 227 nonpregnant control women.

STATISTICAL METHODS

Chi-square test and unconditional logistic regression.

RESULTS

Fifty-three (30.5%) of women with ectopic pregnancy, 18 (15.7%) of pregnant control women and 51 (22.5%) of nonpregnant control women had had one or more previous induced abortions. The adjusted odds ratio of ectopic pregnancy among women with one previous induced abortion was 1.3 (95% confidence interval; 0.9 to 1.8) and 1.2 (95% CI; 0.8 to 1.7) compared with pregnant and nonpregnant control women, respectively. Among women who had two or more induced abortions, the adjusted odds ratio of ectopic pregnancy was 0.2 (95% CI; 0.04 to 0.9) compared with pregnant control women and 1.8 (95% CI; 0.4 to 7.8) compared with nonpregnant control women. When we used the outcome of the most recent pregnancy, birth as reference, we found no association between an outcome of induced abortion and subsequent ectopic pregnancy regardless of whether the control women were pregnant.

CONCLUSION

We found no association between induced abortion and subsequent ectopic pregnancy. Women who had induced abortions were characterized as having several other risk factors for ectopic pregnancy.