Association Between Mental Illness and Risk of Severe Maternal Morbidity in Pregnant Veterans.

OBJECTIVE: Mental illness is a leading cause of maternal mortality, yet population-level research is hindered by limited antenatal mental health data. The Veterans Health Administration, which offers universal outpatient mental health and substance use screening and resources, provides a unique opportunity to assess the effects of antenatal mental illness on severe maternal morbidity (SMM; a composite of life-threatening events around the time of childbirth). METHODS: We conducted a population-level retrospective cohort study of births reimbursed by the Veterans Health Administration in fiscal years 2010-2020. The exposure was antenatal mental illness, identified by International Classification of Disease, Ninth or Tenth Revision, Clinical Modification codes for depression, anxiety, posttraumatic stress disorder, or other serious mental illness, categorized as "active" (coded 1 year or less before childbirth) or "historical" only (coded only more than 1 year before childbirth). The outcome was SMM, defined with the established Health Resources & Services Administration composite. Sequential multivariable Poisson regression models with robust standard errors were conducted, adjusted for sociodemographic confounders. A mediation analysis was conducted to assess the potential contribution of substance use disorders to the relationship between mental illness and SMM. RESULTS: Of 47,883 eligible births, 3.6% of veterans had historical mental illness and 17.4% had active antenatal mental illness. Compared with veterans with no prior mental illness, the risk of SMM was increased in veterans with active mental illness (2.0% vs 1.2%, adjusted risk ratio [aRR] 1.38, 95% CI, 1.15-1.67). There was no significant increase in risk among those with historical mental illness (aRR 0.87, 95% CI, 0.57-1.31). Substance use disorders were not found to be a significant mediator of the association between active mental illness and SMM. CONCLUSION: Active, but not historical, antenatal mental illness was independently associated with higher risk of SMM among pregnant veterans. These findings highlight a potential role for addressing mental health during pregnancy as part of broader efforts to reduce SMM.