Natural history of fibroids in pregnancy: National Institute of Child Health and Human Development Fetal Growth Studies - Singletons cohort

Objective To describe the natural history of fibroids in pregnancy in a racially diverse cohort and explore whether fibroid changes were associated with participant characteristics. Design Prospective cohort study. Setting Twelve clinical sites. Patient(s) Pregnant women (n = 2774; 27% non-Hispanic White, 28% non-Hispanic Black, 29% Hispanic, 17% Asian/Pacific Islander) who had up to 6 obstetric ultrasounds in gestational weeks 10–41. Intervention(s) Sonographers recorded fibroid number and volume of the 3 largest fibroids at each visit. Generalized linear mixed models estimated the trajectories of fibroid number and total volume (overall and stratified by total volume at first visualization: equivalent to a fibroid of <1 cm [small], 1 to <3 cm [medium], or ≥3 cm [large] in diameter). We tested the interactions between the trajectories and race/ethnicity, age (<26, 26–30, 31–34, and ≥35 years), body mass index (<25, 25–29.9, and ≥30 kg/m2), previous miscarriage, parity, and fetal sex, adjusted for total volume at first visualization. Main Outcome Measure(s) Average change in total fibroid volume during pregnancy. Result(s) Overall, 9.6% (266/2,774) of women had a visualized fibroid at any time during pregnancy, including 9% (67/745) of non-Hispanic White women, 14% (106/770) of non-Hispanic Black women, 6% (47/794) of Hispanic women, and 10% (46/465) of Asian or Pacific Islander women. The mean total fibroid volume decreased by 1.0% (95% confidence interval [CI], −1.9%, −0.2%) per week, with a variation in starting total volume. On average, the total volume increased by 2.0% (95% CI, −0.3%, 4.5%) per week among women with small volume; decreased by 0.5% (95% CI, −2.0%, 1.0%) per week among women with medium volume; and decreased by 2.2% (95% CI, −3.4%, −1.0%) per week among women with large volume at first visualization. The volume change also varied by race or ethnicity, parity, age, and miscarriage history. For example, non-Hispanic Black women’s total fibroid volume decreased more than those of non-Hispanic White, Hispanic and Asian/Pacific Islander women (−2.6%, 0.1%, 0.5%, and 0.9% average change per week, respectively). The visualized fibroid number declined on an average by 1.2% per week (95% CI, −1.9%, −0.5%) without significant variation by demographic characteristics. Conclusion(s) The total fibroid volume declined on average throughout pregnancy. However, summarizing across all fibroids disguises substantial heterogeneity by starting total fibroid volume and maternal characteristics. The findings may be a useful reference for clinicians to anticipate how fibroids may change in obstetric patients. Clinical Trial Registration Number NCT00912132. To describe the natural history of fibroids in pregnancy in a racially diverse cohort and explore whether fibroid changes were associated with participant characteristics. Prospective cohort study. Twelve clinical sites. Pregnant women (n = 2774; 27% non-Hispanic White, 28% non-Hispanic Black, 29% Hispanic, 17% Asian/Pacific Islander) who had up to 6 obstetric ultrasounds in gestational weeks 10–41. Sonographers recorded fibroid number and volume of the 3 largest fibroids at each visit. Generalized linear mixed models estimated the trajectories of fibroid number and total volume (overall and stratified by total volume at first visualization: equivalent to a fibroid of <1 cm [small], 1 to <3 cm [medium], or ≥3 cm [large] in diameter). We tested the interactions between the trajectories and race/ethnicity, age (<26, 26–30, 31–34, and ≥35 years), body mass index (<25, 25–29.9, and ≥30 kg/m2), previous miscarriage, parity, and fetal sex, adjusted for total volume at first visualization. Average change in total fibroid volume during pregnancy. Overall, 9.6% (266/2,774) of women had a visualized fibroid at any time during pregnancy, including 9% (67/745) of non-Hispanic White women, 14% (106/770) of non-Hispanic Black women, 6% (47/794) of Hispanic women, and 10% (46/465) of Asian or Pacific Islander women. The mean total fibroid volume decreased by 1.0% (95% confidence interval [CI], −1.9%, −0.2%) per week, with a variation in starting total volume. On average, the total volume increased by 2.0% (95% CI, −0.3%, 4.5%) per week among women with small volume; decreased by 0.5% (95% CI, −2.0%, 1.0%) per week among women with medium volume; and decreased by 2.2% (95% CI, −3.4%, −1.0%) per week among women with large volume at first visualization. The volume change also varied by race or ethnicity, parity, age, and miscarriage history. For example, non-Hispanic Black women’s total fibroid volume decreased more than those of non-Hispanic White, Hispanic and Asian/Pacific Islander women (−2.6%, 0.1%, 0.5%, and 0.9% average change per week, respectively). The visualized fibroid number declined on an average by 1.2% per week (95% CI, −1.9%, −0.5%) without significant variation by demographic characteristics. The total fibroid volume declined on average throughout pregnancy. However, summarizing across all fibroids disguises substantial heterogeneity by starting total fibroid volume and maternal characteristics. The findings may be a useful reference for clinicians to anticipate how fibroids may change in obstetric patients.