Aim To investigate the association between elective caesarean sections and neonatal respiratory morbidity and the importance of timing of elective caesarean sections.

Methods Cohort study with prospectively collected data of all elective Caesarean sections on mothers with a gestational age of 37+0 weeks and more, that were performed in our Hospital from 1 January 2011 to 1 January 2012. Multiple pregnancies, fetuses with congenital anomalies, intrauterine deaths, and emergency Caesarean sections were excluded. Primary outcome measures of neonatal respiratory morbidity included transient tachypnoea of newborn, respiratory distress syndrome, persistent pulmonary hypertension of newborn, serious respiratory morbidity (oxygen therapy for more than two days, nasal continuous positive airway pressure).

Results 568 infants were delivered by elective caesarean section. Compared with newborns intended for vaginal delivery, an increased risk of respiratory morbidity was found for infants delivered by elective caesarean section at 37+0 weeks’ gestation to 37+6 weeks (odds ratio 3.8, 95% confidence interval 2.4 to 6.5), 38+0 weeks’ gestation to 38+6 weeks (3.0, 2.1 to 4.3), and 39+0 weeks’ gestation (1.9, 1.2 to 3.0). The increased risks of serious respiratory morbidity showed the same pattern but with higher odds ratios: a fivefold increase was found at 37 weeks (5.0, 1.6 to 16.0).

Conclusions Infants born by elective caesarean delivery at term are at increased risk for developing respiratory disorders compared with those born by vaginal delivery. A significant reduction in neonatal RDS would be obtained if elective caesarean delivery were performed after 39 + 0 gestational weeks of pregnancy.