Association of Birth Year of Pregnant Individuals With Trends in Hypertensive Disorders of Pregnancy in the United States, 1995-2019

IMPORTANCE: Hypertensive disorders of pregnancy are leading causes of morbidity and mortality among pregnant individuals as well as newborns, with increasing incidence during the past decade. Understanding the individual associations of advancing age of pregnant individuals at delivery, more recent delivery year (period), and more recent birth year of pregnant individuals (cohort) with adverse trends in hypertensive disorders of pregnancy could help guide public health efforts to improve the health of pregnant individuals. OBJECTIVE: To clarify the independent associations of delivery year and birth year of pregnant individuals, independent of age of pregnant individuals, with incident rates of hypertensive disorders of pregnancy. DESIGN, SETTING, AND PARTICIPANTS: This serial cross-sectional study of 38 141 561 nulliparous individuals aged 15 to 44 years with a singleton, live birth used 1995-2019 natality data from the National Vital Statistics System. EXPOSURES: Year of delivery (period) and birth year (cohort) of pregnant individuals. MAIN OUTCOMES AND MEASURES: Rates of incident hypertensive disorders of pregnancy, defined as gestational hypertension, preeclampsia, or eclampsia, recorded on birth certificates. Generalized linear mixed models were used to calculate adjusted rate ratios (aRRs) comparing the incidence of hypertensive disorders of pregnancy in each delivery period (adjusted for age and cohort) and birth cohort (adjusted for age and period) with the baseline group as the reference for each. Analyses were additionally stratified by the self-reported racial and ethnic group of pregnant individuals. RESULTS: Of 38 141 561 individuals, 20.2% were Hispanic, 0.8% were non-Hispanic American Indian or Alaska Native, 6.5% were non-Hispanic Asian or Pacific Islander, 13.9% were non-Hispanic Black, and 57.8% were non-Hispanic White. Among pregnant individuals who delivered in 2015 to 2019 compared with 1995 to 1999, the aRR for the incidence of hypertensive disorders of pregnancy was 1.59 (95% CI, 1.57-1.62), adjusted for age and cohort. Among pregnant individuals born in 1996 to 2004 compared with 1951 to 1959, the aRR for the incidence of hypertensive disorders of pregnancy was 2.61 (95% CI, 2.41-2.84), adjusted for age and period. The incidence was higher among self-identified non-Hispanic Black individuals in each birth cohort, with similar relative changes for period (aRR, 1.76 [95% CI, 1.70-1.81]) and cohort (aRR, 3.26 [95% CI, 2.72-3.91]) compared with non-Hispanic White individuals (period: aRR, 1.60 [95% CI, 1.57-1.63]; cohort: aRR, 2.53 [95% CI, 2.26-2.83]). CONCLUSIONS AND RELEVANCE: This cross-sectional study suggests that more recent birth cohorts of pregnant individuals have experienced a doubling of rates of hypertensive disorders of pregnancy, even after adjustment for age and delivery period. Substantial racial and ethnic disparities persisted across generations.