Tubal Pregnancy and Cigarette Smoking: Is There an Association?

Abstract

This study was undertaken to assess the relationship between cigarette smoking and ectopic pregnancy. A case-control study, with data from the Women's Health Study (WHS), was used to evaluate this relationship. In the WHS, women were interviewed by means of structured questionnaires between April 1977 and August 1978 in 16 hospitals in nine U.S. cities. A total of 169 ectopic pregnancy patients were identified. Control women included 293 women who had delivered after a normal pregnancy and 88 prenatal women. We compared women who reported that they smoked at conception with women who reported that they had never smoked. The final data set included 133 ectopic pregnancy cases and 341 controls. The crude risk of ectopic pregnancy was slightly greater for women who smoked at conception than for women who had never smoked [odds ratio (OR) 1.2, confidence interval (CD 0.81–1.8]. When we controlled for age, race, prior use of IUD, and number of recent sexual partners, the OR decreased to 1.1 (CI 0.73–1.7). Previous studies have reported an increased risk of ectopic pregnancy associated with smoking. Our study showed no increased risk. Given the various mechanisms involved with the effect of cigarette smoking on the hormonal system, ciliary transport in the fallopian tubes, and immune system, it is intriguing that we did not find an increased risk of ectopic pregnancy. Additional studies are needed to determine those risk factors that can be effectively modified to decrease ectopic pregnancy.