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.