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.