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

Purpose: We examined whether increasing severe maternal morbidity (SMM) rates are driven by changes in maternal age distribution or age-specific SMM rates. Methods: 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. Results: 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. Conclusion: 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.