Racial Differences in Adverse Pregnancy Outcomes and Incident Hypertension: A Mediation Analysis

Adverse pregnancy outcomes (APOs) are associated with increased hypertension risk. Black women experience higher rates of APOs and hypertension compared with White women, but whether APOs contribute to Black-White hypertension disparities remains unknown.

The nuMoM2b-HHS (Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-To-Be-Heart Health Study) prospectively recruited nulliparous pregnant people at 8 US centers (2010-2013) with follow-up 2 to 7 years postpartum (2014-2017). Race, which represents a social construct, was self-identified. The primary outcome was incident hypertension at follow-up. APOs included hypertensive disorders of pregnancy, preterm birth, and small-for-gestational age birth. Potential confounders (psychological health, social factors, and health behaviors) were assessed via validated questionnaires. We used targeted maximum likelihood-based estimation to estimate Black-White hypertension differences that would remain if racial disparities in APOs were eliminated.

Among 3335 participants (17% Black; 83% White; mean [SD] age, 27.6 [5.1] years), APO incidence was higher in Black versus White individuals (rate differences [RDs] per 1000 births: hypertensive disorders of pregnancy: 52.5 [95% CI, 20.0-85.1]; preterm birth: 45.4 [95% CI, 20.8-70.1]; small-for-gestational age: 102.4 [95% CI, 75.8-129.1]). Incident hypertension at median 3 years postpartum was higher in Black versus White individuals (RD, 107.1 [95% CI, 69.6-144.4]). APOs mediated the racial disparity in hypertension; eliminating Black-White disparities in APOs would decrease the Black-White disparity in hypertension by 18.2% for hypertensive disorders of pregnancy (RD, 87.6 [95% CI, 36.1-139.2]), 16.3% for preterm birth (RD, 89.6 [95% CI, 41.7-137.6]), and 13.9% for small-for-gestational age (RD, 92.2 [95% CI, 41.6-142.9]).

Black-White differences in hypertension were partially mediated by APOs. APOs may represent a pregnancy-specific pathway contributing to racial disparities in hypertension.