Does Delayed Fertility Explain the Rise in Comorbidities Among the Birthing Population?

Background: The increasing prevalence of preexisting health conditions among pregnant people is often attributed to the concurrent rise in maternal age. However, the link between advanced maternal age (AMA) and increases in chronic conditions among the birthing population has not been systematically documented at the population level. Materials and Methods: This retrospective population-based cohort study was based on linked hospitalization discharge and birth certificate data for live birth deliveries in California from 1991 to 2012. Decomposition techniques evaluated whether changes in the prevalence of selected preexisting health conditions during delivery (autoimmune conditions, chronic hypertension, cardiac disease, diabetes, and renal disease) were explained by population-level increases in maternal age. Analyses further adjusted for maternal education, plurality, insurance status, and availability of paternal information on the birth certificate. Results: Between 1991 and 2012, there were more than 11.5 million live birth deliveries in California. AMA (≥35 years) increased nearly 70% over this period. The prevalence of autoimmune conditions, chronic hypertension, diabetes, and renal disease rose among the birthing population, while cardiac disease declined. The prevalence of all conditions was higher for AMA, but changes in maternal age accounted for only 5.3%, 8.4%, 13.9%, and 0.4%, of the increase in autoimmune conditions, chronic hypertension, diabetes, and renal disease, respectively. Conclusion: While AMA was associated with higher rates of preexisting health conditions, it contributed little to the increase in autoimmune conditions, chronic hypertension, and diabetes and nothing to the rise in renal disease during childbirth.