A population-based study to identify the prevalence and correlates of the dual burden of severe maternal morbidity and preterm birth in California

Background: Prior studies have documented associations between preterm birth and severe maternal morbidity (SMM) but the prevalence and correlates of dual burden are not adequately understood, despite significant family implications. Purpose: To describe the prevalence and correlates of the dual burden of SMM and preterm birth and to understand profiles of SMM by dual burden of preterm birth. Approach: This retrospective cohort study included all California live births in 2007-2012 with gestations 20-44 weeks and linked to a birth cohort database maintained by the California Office of Statewide Health Planning and Development (n = 3,059,156). Dual burden was defined as preterm birth (<37 weeks) with severe maternal morbidity (SMM, defined by Centers for Disease Control). Predictors for dual burden were assessed using Poisson logistic regression, accounting for hospital variance. Results: Rates of preterm birth and SMM were 876 and 140 per 10,000 births, respectively. The most common indications of SMM both with and without preterm birth were blood transfusions and a combination of cardiac indications. One-quarter of women with SMM experienced preterm birth with a dual burden rate of 37 per 10,000 births. Risk of dual burden was over threefold higher with cesarean birth (primiparous primary aRR = 3.3, CI = 3.0-3.6; multiparous primary aRR = 8.1, CI = 7.2-9.1; repeat aRR = 3.9, CI = 3.5-4.3). Multiple gestation conferred a six-fold increased risk (aRR = 6.3, CI = 5.8-6.9). Women with preeclampsia superimposed on gestational hypertension (aRR = 7.3, CI = 6.8-7.9) or preexisting hypertension (aRR = 11.1, CI = 9.9-12.5) had significantly higher dual burden risk. Significant independent predictors for dual burden included smoking during pregnancy (aRR = 1.5, CI = 1.4-1.7), preexisting hypertension without preeclampsia (aRR = 3.3, CI = 3.0-3.7), preexisting diabetes (aRR = 2.6, CI = 2.3-3.0), Black race/ethnicity (aRR = 2.0, CI = 1.8-2.2), and prepregnancy body mass index <18.5 (aRR = 1.4, CI = 1.3-1.5). Conclusions: Dual burden affects 1900 California families annually. The strongest predictors of dual burden were hypertensive disorders with preeclampsia and multiparous primary cesarean.