Contribution of Maternal Age to Increasing Severe Maternal Morbidity During Birth and Up to 1 Year Postpartum

We examined whether increasing severe maternal morbidity (SMM) rates are driven by changes in maternal age distribution or age-specific SMM rates. In a retrospective cohort study across three states, we analyzed data from two time points (2008-2009 to 2019-2020). We used Kitagawa decomposition analysis to determine the contributions of changes in maternal age distribution and age-specific SMM rates to SMM rates both with and without transfusion during birth and up to 1 year postpartum, stratified by race/ethnicity. We examined the following racial/ethnic groups: non-Hispanic white, non-Hispanic Black, Hispanic, and non-Hispanic Asian/Pacific Islander. Between 2008-2009 and 2019-2020, SMM and non-transfusion SMM rates increased from 213.6 to 260.5 and from 109.6 to 154.8 per 10,000 births, respectively. Across all racial and ethnic groups, the proportion of younger birthing individuals (<25 years) decreased and the proportion of older individuals (≥30 years) increased. The decomposition analysis showed that increases in SMM and non-transfusion SMM were primarily due to increases in age-specific SMM rates (100.0% and 94.6%, respectively), particularly among younger birthing individuals. Changes in maternal age distribution had a minimal overall contribution. However, when stratified by race/ethnicity, changes in maternal age distribution had a greater contribution to SMM (28.9%) and non-transfusion SMM (22.7%) rates among non-Hispanic Black individuals, with little to no contribution observed in the other groups. The increasing rates of birth-related and postpartum SMM rates stem from increasing rates of SMM in every age group rather than shifts in maternal age distribution.