Elective C-section increases by up to fourfold the risk of respiratory morbidity in babies who were delivered at 37–39 weeks of gestation, compared with babies who were delivered vaginally or by emergency C-section at the same gestational age.
That finding—from a Danish cohort study of 34,458 singleton deliveries—suggests that elective C-section should wait until after the 39th week, the study investigators wrote online in BMJ.
“Carrying out elective caesarean sections at greater gestational ages may, however, result in higher rates of intrapartum caesarean sections because some women would go into spontaneous labour (in our population, 25% of spontaneous intended vaginal deliveries started before 39 weeks' gestation),” wrote Anne Kirkeby Hansen of the Aarhus (Denmark) University Hospital and associates.
“Compared with elective caesarean sections, intrapartum caesarean sections may carry an increased risk of complications such as uterine rupture in women with previous caesarean section, infections, or even maternal mortality,”
The risk of respiratory morbidity (transitory tachypnea of the newborn, respiratory distress syndrome, persistent pulmonary hypertension of the newborn) was increased in babies delivered by elective C-section at 37 weeks (odds ratio 3.9), 38 weeks (OR 3.0), and 39 weeks (OR 1.9), compared with newborns intended for vaginal delivery.
Risk was not increased at 40 weeks (OR 0.9).
The data were adjusted for factors such as smoking and parity, the study authors reported (doi:10.1136/bmj.39405.539282.BE).
The analysis included all liveborn singletons born without malformation between 37 and 41 weeks' gestation at one institution between 1998 and 2006.
In all, 2,687 liveborn babies were delivered by elective C-section and 2,877 were delivered by emergency C-section. The remaining babies were born vaginally.
A total of 1.8% of all babies had a respiratory problem, with 0.2% of them having serious respiratory morbidity (a condition requiring treatment for at least 3 days with continuous oxygen supplementation, nasal continuous positive airway pressure, or any period of mechanical ventilation).
The relative risk for serious respiratory morbidity was increased in those delivered by elective C-section at 37 weeks (OR 5.0) and 38 weeks (OR 4.2), compared with intended vaginal delivery.
At 39 weeks, the odds ratio was 2.4, but this increase in risk was not statistically significant.
The authors said hormones released during normal vaginal delivery may help prevent respiratory problems.
Catecholamines are present in the fetus during normal vaginal delivery in response to the rupture of membranes and labor, a phenomenon that may decrease the secretion of fetal lung liquid, increase its absorption, and stimulate the release of surfactants.