The association of pregnancy with outcomes among critically ill reproductive-aged women: A propensity-score matched retrospective cohort analysis

Background The maternal mortality rate in the US is unacceptably high. However, the relative contribution of pregnancy to these outcomes is unknown. Studies comparing outcomes among pregnant versus non-pregnant critically ill patients show mixed results and are limited by small sample sizes. Research question What is the association of pregnancy with critical illness outcomes? Study design and methods We performed a retrospective cohort study of 18-55-year-old women who received invasive mechanical ventilation (MV) on hospital day 0 or 1, or had sepsis present on admission (infection with organ failure) discharged from Premier Healthcare Database hospitals in 2008-2021. The exposure was pregnancy. The primary outcome was in-hospital mortality. We created propensity scores for pregnancy (using patient and hospital characteristics) and performed 1:1 propensity-score matching without replacement within age strata (to ensure exact age matching). We performed multilevel multivariable mixed-effects logistic regression for propensity-matched pairs with pair as a random effect. Results 3,093 pairs were included in the matched MV cohort, and 13,002 in the sepsis cohort. Cohort characteristics in both were well-balanced (all standard mean differences<0.1). Among matched pairs, unadjusted mortality was 8.0% versus 13.8% for MV and 1.4% versus 2.3% for sepsis, among pregnant and non-pregnant patients, respectively. In adjusted regression, pregnancy was associated with lower odds of in-hospital mortality (MV: odds ratio [OR] 0.50, 95% confidence interval [CI] 0.41-0.60, p<0.001; sepsis: OR 0.52, 95% CI 0.40-0.67, p<0.001). Interpretation In our large US cohort, critically ill pregnant women receiving MV or with sepsis had better survival than propensity score-matched, non-pregnant women. These findings must be interpreted in the context of likely residual confounding.