There are conflicting results in the literature on the impact of chorioamnionitis on neonatal respiratory morbidities. However, most studies are based on small clinical samples and fail to account for the competing risk of perinatal death. This study aimed to determine whether chorioamnionitis affects the incidence of respiratory distress syndrome (RDS) and bronchopulmonary dysplasia (BPD) after accounting for the increased risk of death.

Retrospective cohort study using linked birth and infant death registration and hospitalization records from Washington State between 2002 and 2011 (n = 763,671 singleton infants and n = 56,537 singleton preterm infants). Logistic regression models based on the traditional and fetuses-at-risk approaches were used to model two composite outcomes namely RDS and perinatal death and BPD and perinatal death. Confounders adjusted for in the models included maternal age, race, diabetes, hypertension, antenatal corticosteroids, mode of delivery and infant sex.

While models using the traditional approach found a significant association only between chorioamnionitis and composite BPD and perinatal death (OR = 1.23, 95% CI: 1.01–1.50); using the fetuses-at-risk approach, there was a significant association between chorioamnionitis and both composite outcomes (RDS and perinatal death OR = 2.74, 2.50–3.01; BPD and perinatal death OR = 5.18, 95% CI: 4.39–6.11).

The fetuses-at-risk approach models the causal impact of chorioamnionitis on the development of the fetal lung and shows an increased risk of RDS, BPD and perinatal death associated with such maternal infection.