The impact of Severe Maternal Morbidity on probability of subsequent birth in a population-based study of women in California from 1997-2017

Importance: Complications during pregnancy and birth can impact whether an individual has more children. Individuals experiencing SMM are at a higher risk of general and reproductive health issues after pregnancy, which could reduce the probability of a subsequent birth. Objective: To examine whether experiencing SMM during an individual's first birth affects their probability of having an additional birth, and whether this effect varies by maternal factors. Methods: This retrospective cohort study US linked vital records and maternal discharges from 1997 to 2017 to identify all California births. The exposure, Severe Maternal Morbidity (SMM) was identified using a Centers for Disease Control and Prevention index. Individuals whose first birth was a singleton live birth were followed until their second birth or December 31, 2017, whichever came first. Hazard ratios for having a subsequent birth were estimated using Cox proportional hazard regression models. This association was assessed overall and stratified by maternal factors of a priori interest: age, race/ethnicity, and payer. Results: Of the 3,916,413 individuals in our study, 51,872 (1.3%) experienced SMM at first birth. Compared to those who do not experience SMM, individuals who had SMM had a lower hazard, or instantaneous rate, of subsequent birth (adjusted HR 0.83, 95% CI: 0.82, 0.84); this association was observed in all levels of stratification (for example, adjusted HR range for known race/ethnicity: 0.78, 95% CI: 0.76, 0.80 for non-Hispanic White to 0.90, 95% CI: 0.88, 0.92 for Hispanic) and all indicators of SMM (0.24, 95% CI: 0.17, 0.35 for cardiac arrest/ventricular fibrillation to 0.84, 95% CI: 0.80, 0.87 for eclampsia). Conclusion and Relevance: Our findings suggest that individuals who experience SMM at the time of their first birth are less likely to have a subsequent birth as compared to those who do not experience SMM at the time of their first birth. While the reasons for these findings are unclear, they could inform reproductive life planning discussions for individuals experiencing SMM. Future directions include studies exploring the reasons for not having a subsequent birth.