Association between gestational age and severe maternal morbidity in preterm delivery: A nationwide population-based cohort study.

Objective: This study investigates whether early gestational age (GA) at delivery is associated with an increased risk for severe maternal morbidity (SMM) in women with preterm delivery.

Methods: This retrospective national cohort study based on the Programme de Médicalisation des Systèmes d'Information database included mothers who gave birth between 22 and 37 weeks in metropolitan France in 2019 (in utero deaths and medical terminations of pregnancies were excluded). SMM was defined as a composite criterion consisting of the occurrence of at least one of the following events: death, severe preeclampsia, obstetric surgical complications, severe maternal diseases, and admission to the intensive care unit. The association between GA as a categorical variable (22-24 weeks, 24-26 weeks, 26-28 weeks, 28-32 weeks, 32-34 weeks, and >34 weeks) and SMM was assessed by performing multivariate logistic regressions. Interaction tests were performed to identify factors that might influence the association between SMM and GA.

Results: Among the 42 821 women who gave birth prematurely in metropolitan France in 2019 (6.2% of all parturients), 6249 (1.6%) presented with an SMM event (mostly severe preeclampsia, at 74.3%). GA was associated with SMM (adjusted odds ratio ranging from 1.83 between 32 and 34 weeks to 2.67 between 22 and 24 weeks compared to the reference group of 34-37 weeks, P < 0.001). The evolution of the risk of SMM according to GA appeared linear.

Conclusion: Early GA at delivery was associated with an increased risk of SMM in women with preterm delivery. This study showed that SMM is also increased in cases of spontaneous prematurity and vaginal delivery.