Risk of uterine leiomyomata according to birthplace and geographic region in the black womenʹs health study

Purpose Uterine leiomyomata (fibroids) are a major source of gynecologic morbidity among U.S. black women. We prospectively examined the incidence of self-reported uterine leiomyomata by birthplace and geographic region in the Black Womenʹs Health Study, a nationwide follow-up study of U.S. black women. Methods From 1997 to 2001, we followed 20,451 premenopausal women with intact uteri and no prior diagnosis of leiomyomata. Cox regression models, stratified by age and time period, were used to derive rate ratios (IRRs) and 95% confidence intervals (CIs) for the associations of interest while adjusting for potential confounders. Results After 68,580 person-years of follow-up, 2049 ultrasound- or hysterectomy-confirmed cases were reported. Compared with women living in the West, multivariate IRRs for women living in the Northeast, South, and Midwest were 1.20 (95% CI = 1.05–1.38), 1.24 (95% CI = 1.09–1.42), and 1.09 (95% CI = 0.95–1.26), respectively. The multivariate IRR comparing women who were foreign born to U.S. born was 1.21 (95% CI = 1.01–1.45). Among the U.S.-born women, risk did not differ according to parents place of birth. Conclusion Our data are the first to provide evidence that incidence of uterine leiomyomata may vary according to birthplace and geographic region in U.S. black women. Control for Pap smear screening and established risk factors for uterine leiomyomata did not account for these findings.