In utero exposures and the incidence of endometriosis

Abstract

Objective: To investigate the relation between the fetal environment and endometriosis. Design: Prospective cohort study.Setting: Nurses' Health Study II with 10 years of follow-up.Participant(s): Eighty-four thousand, four hundred forty-six women aged 25-42 who had never been diagnosed with endometriosis, infertility, or cancer at baseline in 1989. Main Outcome Measure(s): Incidence of laparoscopically confirmed endometriosis according to birthweight, prematurity, multiple gestation, diethylstilbestrol (DES) exposure, and having been breastfed. Result(s): During 566,250 woman-years of follow-up, 1,226 cases of laparoscopically-confirmed endometriosis were reported among women with no past infertility. After adjusting for age, calendar time, parity, race, and body mass index at age 18, we observed a linear increase in the incidence rate with decreasing birthweight (rate ratio [RR] = 1.3 for birthweight <5.5 pounds versus 7.0-8.4 pounds, 95% confidence interval [CI] = 1.0-1.8, P value, test for trend = .01). In addition, women who were born as one of a multiple gestation (i.e., twins or greater number) were at increased risk even after controlling for birthweight (RR = 1.7, CI = 1.2-2.5). The rate of endometriosis was also 80% greater among women exposed to diethylstilbestrol in utero (RR = 1.8, CI = 1.2-2.8). Neither premature delivery nor having been breastfed were associated with the incidence of endometriosis. None of these effect estimates were modified by infertility status at the time of endometriosis diagnosis.Conclusion(s): The fetal environment is associated with subsequent laparoscopically confirmed endometriosis in this cohort of US women.