LAUSR

BACKGROUND Uterine fibroids are common. Symptoms are debilitating for many, leading to high medical and societal costs. Indirect data suggest that compared to white women, African-Americans develop fibroids at least ten years earlier on average, and their higher health burden has been well documented. OBJECTIVE To directly measure fibroid incidence and growth in a large, community-based cohort of young African-American women. STUDY DESIGN This observational, community-based, prospective study enrolled 1693 African American women, ages 23-35 with no prior diagnosis of fibroids. Standardized transvaginal ultrasound examinations at enrollment and after approximately 18-months were conducted to identify and measure fibroids ≥0.5 cm in diameter. Fibroid growth (change in natural log volume per 18 months) was analyzed with mixed model regression (n = 344 fibroids from 251 women whose baseline ultrasound revealed already existing fibroids). RESULTS Among the 1123 fibroid-free women with follow-up data (88% were followed), incidence was 9.4% (95% confidence interval, CI=7.7,11.2) and increased with age (ptrend=<0.0001), from 6% (CI=3,9) for 23-25 year-olds to 13% (CI=9,17) for 32-35 year-olds. The chance of any new fibroid development was over twice as high for women with existing fibroids compared to women who were fibroid-free at baseline (age-adjusted relative risk = 2.3, (CI=1.7,3.0). The uterine position of most incident fibroids (60%) was intramural corpus. Average fibroid growth was 89% per 18 months (CI=74%,104%), but varied by baseline fibroid size (p<0.0001). Fibroids ≥2 cm in diameter had average growth rates well under 100%. In contrast, small fibroids (<1 cm diameter) had an average growth rate of nearly 200% (188%, CI=145%,238%). However, these small fibroids also had a high estimated rate of disappearance (23%). CONCLUSIONS This is the first study to directly measure age-specific fibroid incidence with a standardized ultrasound protocol and to measure fibroid growth in a large community-based sample. Findings indicate that very small fibroids are very dynamic in their growth, with rapid growth, but a high chance of loss. Larger fibroids grow more slowly. For example, a 2-cm fibroid is likely to take 4-5 years to double its diameter. Detailed data on fibroid incidence confirm an early onset in African American women.