Objective: To estimate the proportion of pregnant women with one or more leiomyomas detected by research-quality ultrasound screening in the first trimester, to describe the size and location of leiomyomas identified, and to report variation in prevalence by race/ethnicity.
Methods: Within an ongoing prospective cohort, we conducted 4,271 first-trimester or postmiscarriage ultrasound examinations. Sonographers measured each leiomyoma three separate times, recording the maximum diameter in three perpendicular planes each time. Sonographers and investigators classified type and location.
Results: Among 458 women with one or more leiomyomas (prevalence 10.7%), we identified a total of 687 leiomyomas. The mean size of the largest leiomyoma was 2.3 cm (95% confidence interval [CI] 1.8-2.8). Mean gestational age at ultrasonography was 61+/-13 days from last menstrual period. Prevalence varied by race/ethnicity: 18% in African-American women (95% CI 13-25), 8% in white women (95% CI 7-11), and 10% in Hispanic women (95% CI 5-19). The proportion of women with leiomyomas increased with age much more steeply for African-American women than for white women.
Conclusion: Leiomyomas are common in pregnancy and occur more often among African-American women. Given the limited research on effects of leiomyomas on reproductive outcomes, the degree to which race/ethnic disparities in prevalence of leiomyomas may contribute to disparities in events such as miscarriage and preterm birth warrants investigation.