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

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.

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.

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).

Dual burden affects 1900 California families annually. The strongest predictors of dual burden were hypertensive disorders with preeclampsia and multiparous primary cesarean.