Recurrent Severe Maternal Morbidity in an Obstetric Population With a High Comorbidity Burden

Objective: To evaluate the risk of severe maternal morbidity (SMM) in subsequent pregnancies in patients who experienced SMM in a previous pregnancy compared with those who did not.

Methods: We conducted a retrospective cohort study of patients with two or more deliveries at 23 or more weeks of gestation at a single Southeastern U.S. tertiary care center between 2015 and 2018. The primary exposure was SMM including transfusion (transfusion SMM) in a previous pregnancy, as defined by the Centers for Disease Control and Prevention, using International Classification of Diseases, Ninth or Tenth Revision codes. The primary outcome was transfusion SMM in any subsequent pregnancy in the study time frame. Generalized estimating equation models were used to estimate the relative risk (RR) and associated 95% CIs of transfusion SMM in patients with transfusion SMM in a prior pregnancy compared with patients without transfusion SMM in a previous pregnancy. Severe maternal morbidity without transfusion (nontransfusion SMM) and cross-analysis to determine risk of a different type of SMM after a history of SMM were analyzed similarly.

Results: Of 852 included patients, transfusion SMM and nontransfusion SMM occurred in 90 (10.6%) and 18 (2.1%), respectively, in the first captured pregnancy and in 79 (9.3%) and 9 (1.1%), respectively, in subsequent pregnancies. Anemia (34.6-40.0%), obesity (33.4-40.4%), substance use disorder (14.2-14.6%), and preeclampsia (12.0-11.4%) were the most prevalent morbidities at first captured and subsequent pregnancies, respectively. There was a 16-fold higher risk of transfusion SMM in a subsequent pregnancy after experiencing transfusion SMM in the first captured pregnancy (57.8% vs 3.5%, RR 16.3 95% CI, 10.8-24.6). Nontransfusion SMM was similarly higher in patients with nontransfusion SMM in their first captured pregnancy compared with those without (16.7% vs 0.7%, RR 23.2 95% CI, 6.3-85.4). Additionally, patients who experienced transfusion SMM in their first captured pregnancies were at sixfold higher risk of developing nontransfusion SMM in a subsequent pregnancy (RR 6.2, 95% CI, 1.7-22.6). However, in cross-analysis of patients who experienced nontransfusion SMM, the risk of transfusion SMM in a subsequent pregnancy was not statistically significant.

Conclusion: The risks of SMM in subsequent pregnancies after previous SMM are extremely high and are higher than previous estimates. Future studies should estimate the contributions of comorbidities and other structural determinants including social vulnerability to help design interventions to reduce subsequent pregnancy risks.