Uterine fibroids and risk of hypertensive disorders of pregnancy; results from a racially diverse high-risk cohort

Study Question: What is the impact of the presence of uterine fibroids on the risk of developing hypertensive disorders of pregnancy (HDP) in a predominantly urban, low-income, Black, and Hispanic population of women with ultrasound or clinically diagnosed uterine fibroids with rich phenotypic data to carefully control for potential confounders? Summary answers: The odds of HDP were 39% higher in women with uterine fibroids compared to those without when controlled for age at delivery, race, prepregnancy BMI, education, parity, and smoking status; neither fibroid location or size modified this risk. What is known already: Studies are conflicting regarding the impact of uterine fibroids on risk of HDP; limitations of prior studies include primarily Western European populations and lack of measurement of potential confounders. Study design, size, and duration: A total of 7030 women from the Boston Birth Cohort (a racially diverse cohort recruited from 1998 to 2018) that had clinical and ultrasound data regarding uterine fibroid status were included in this analysis. Participants/materials, setting, and methods: Four hundred eighty-nine women with uterine fibroids and 6541 women without were included. Hypertensive disorders of pregnancy were ascertained from medical records. Logistic regression was performed to assess the risk of HDP in women with and without uterine fibroids. Covariates adjusted for included age at delivery, race, pre-pregnancy BMI, education, parity, and smoking status during pregnancy. Sub-analyses were performed to assess the impact of specific fibroid location and overall fibroid volume burden. Main results and the role of chance: The incidence of uterine fibroids in the cohort was 7% (N=489). Twelve percent of women without uterine fibroids and 17% of women with fibroids developed HDP; in multivariate analyses adjusted for the potential confounders above, the odds of HDP were 39% higher in women with uterine fibroids compared to those without (p=0.03). Women with a uterine fibroid diagnosis based on ICD code (n=297) versus asymptomatic incidental ultrasound diagnosis (n=192) had a significantly greater chance of developing HDP (20 vs 15%, p=0.006). There did not appear to be an association between number of fibroids or total fibroid volume and the risk of developing HDP. Limitations, reasons for caution: This study has a relatively small sample size. While post-hoc power calculation determined that there was adequate power to detect a 4.6% difference in the incidence of development of HDP between participants with uterine fibroids and those without, the sub-analyses based on fibroid size, location, and method of diagnosis were underpowered to determine a similar level of difference. Wider implications of the findings: In a racially diverse cohort, presence of uterine fibroids was a significant risk factor for developing HDP, regardless of uterine fibroid size or location. This may have implications for additional monitoring and risk stratification in women with uterine fibroids. Study funding/competing interests: KC supported by WRHR NIH NICHD Award # K12 HD103036, PI Andrew Satin, RD James Segars. The Boston Birth Cohort (the parent study) was supported in part by the National Institutes of Health (NIH) grants (2R01HD041702, R01HD098232, R01ES031272, R01ES031521, and U01 ES034983); and the Health Resources and Services Administration (HRSA) of the U.S. Department of Health and Human Services (HHS) (UT7MC45949). This information or content and conclusions are those of the authors and should not be construed as the official position or policy of, nor should any endorsements be inferred by any funding agencies. Trial registration number: The BBC is registered under clinicaltrials.gov NCT03228875.