Risk factors for the recurrence of severe maternal morbidity in first and second births in California, 1997 to 2020

Prior research on severe maternal morbidity shows an elevated risk of recurrence but has not investigated if it varies by sociodemographic subgroups or by severe maternal morbidity subtype.

To examine the recurrence risk of severe maternal morbidity and severe maternal morbidity subtypes among specific subgroups, such as age, race/ethnicity, educational status, and insurance status.

We used vital records (live birth and fetal death certificates) from 1997 to 2020 that were linked to maternal hospital discharge records to identify 1,989,104 first and second birth pairs. The outcomes, severe maternal morbidity and nontransfusion severe maternal morbidity, were identified using International Classification of Diseases, Ninth/10th Revision codes for 21 indicators and further categorized into 8 subtypes based on the organ systems impacted (cardiac severe maternal morbidity, renal severe maternal morbidity, respiratory severe maternal morbidity, hemorrhage severe maternal morbidity, sepsis severe maternal morbidity, other obstetric severe maternal morbidity, other medical severe maternal morbidity, and transfusion severe maternal morbidity). We used sequentially adjusted modified Poisson regression model with bootstrapped errors to estimate the recurrences of composite severe maternal morbidity, severe maternal morbidity subtypes, and severe maternal morbidity indicators between first and second birth. Risk ratios were stratified by the following: age, education, insurance, interpregnancy interval, nativity, plurality, race/ethnicity, and the Expanded Obstetric Comorbidity Index.

The recurrence risk ratio of overall severe maternal morbidity and nontransfusion severe maternal morbidity between first and second births were 3.4 (95% confidence interval, 2.9-4.1) and 3.7 (95% confidence interval, 2.6-5.3), respectively, adjusted for sociodemographic and clinical factors. Among the severe maternal morbidity subtypes, the adjusted risk of recurrence was particularly elevated among individuals who experienced other medical severe maternal morbidity (adjusted risk ratio, 119; 95% confidence interval, 30-267) and cardiac severe maternal morbidity (adjusted risk ratio, 32.6; 95% confidence interval, 6.6-88.4). In stratified analyses, recurrence risk ratios were highest among individuals with higher education, private insurance, singleton pregnancies, and lower comorbidity scores (all groups with lower absolute prevalence of severe maternal morbidity). Hispanic populations had a notably lower recurrence risk ratio for severe maternal morbidity compared with White, Black, and Asian subgroups. For nontransfusion severe maternal morbidity, Black individuals were the only group that had both higher absolute prevalence and higher recurrence risk ratios for nontransfusion severe maternal morbidity (relative to other racial and ethnic subgroups).

The recurrence risk of severe maternal morbidity and nontransfusion severe maternal morbidity varies by severe maternal morbidity subtypes as well as among sociodemographic subgroups. This recurrence risk remains elevated after adjustment for sociodemographic and clinical factors. We identify subgroups among whom additional counseling and monitoring may be warranted after an initial severe maternal morbidity occurrence, if additional pregnancies are desired. Some groups that typically have a lower absolute prevalence of severe maternal morbidity had higher recurrence risk ratios relative to their counterparts, which suggests the importance of close monitoring for the potential recurrence of severe maternal morbidity regardless of baseline prevalence based on known risk factors.