Chorioamnionitis and adverse outcomes in low-risk pregnancies: a population-based study

To compare the composite neonatal and maternal adverse outcomes among low-risk pregnancies with versus without chorioamnionitis.

We conducted a retrospective cohort study using U.S. Vital Statistics Data. The study population was restricted to full term, low-risk, singleton pregnancies. Pregnancies were categorized into those affected and unaffected by chorioamnionitis. The primary outcome was composite neonatal adverse outcome and the secondary outcome was composite maternal adverse outcome. Multivariable Poisson regression models with robust error variance were used to examine the factors associated with chorioamnionitis and to evaluate the association between chorioamnionitis and adverse outcomes [using adjusted relative risk (aRR) and 95% confidence interval (CI)].

Of 19.7 million live births, 59.4% met inclusion criteria; among them, 1.7% were complicated by chorioamnionitis. The risk of composite neonatal adverse outcome was higher in newborns delivered by women with chorioamnionitis (aRR = 3.40; 95% CI = 3.30-3.49). Compared to women without chorioamnionitis, those with chorioamnionitis had a higher risk of composite maternal adverse outcome (aRR = 2.42; 95% CI = 2.31-2.55). Infant mortality was also higher in affected pregnancies (aRR = 1.23; 95% CI = 1.09-1.38).

Among low-risk pregnancies, chorioamnionitis is associated with a higher risk of composite neonatal and maternal adverse outcomes. Infant death is also increased.