Babies delivered by elective caesarean section around term carry up to a fourfold increased risk of breathing problems compared with babies delivered vaginally or by emergency caesarean section, concludes a study from Denmark published on bmj.com today.

The rate of delivery by elective caesarean section is increasing. Previous studies have shown that elective caesareans are linked to an increased risk of newborn respiratory problems.

The exact reasons for this are unknown, but one explanation is that hormonal and physiological changes associated with labour are necessary for lungs to mature and that these changes may not be present in infants delivered by elective caesarean section. Gestational age at the time of elective caesarean section may also be important.

So researchers at Aarhus University Hospital in Denmark investigated the association between elective caesarean sections and newborn respiratory problems. They also analysed the importance of timing of elective caesarean sections.

Over 34,000 live born singleton babies without birth defects and with gestational ages of 37 to 41 weeks were included in the main analysis. Deliveries were categorised into two groups: elective caesarean section and intended vaginal delivery (i.e. all vaginal deliveries and emergency caesarean sections).

Factors that could affect the results, such as maternal smoking and alcohol intake during pregnancy, maternal body mass index, maternal age and education, were also taken into account.

2,687 infants were delivered by elective caesarean section. Compared with infants intended for vaginal delivery, infants delivered by elective caesarean section were found to have an increased risk of general respiratory problems.

This risk increased the earlier the caesarean was performed. A nearly fourfold increased risk was found at 37 weeks gestation, a threefold increase in risk at 38 weeks gestation, and a doubling of risk in infants delivered at 39 weeks gestation. Adjusting for maternal factors had little effect.

For example, at 37 weeks, 2.8% of infants delivered by intended vaginal delivery had general respiratory problems compared to 10% of infants delivered by elective caesarean section. At 38 weeks, the proportion was 1.7% compared to 5.1% and at 39 weeks, 1.1% compared to 2.1%.

The risks of serious respiratory problems showed the same pattern but with higher risk estimates than those for general respiratory problems.

Analyses after restriction to low risk pregnancies revealed slightly smaller risk estimates at 37 weeks gestation but essentially unchanged estimates at 38 and 39 weeks gestation for serious respiratory problems, whereas the estimates remained unchanged at all gestational ages for general respiratory problems.

Babies delivered by elective caesarean section at 37 to 39 weeks of gestation carry a two to fourfold increased risk of respiratory morbidity compared with babies delivered by intended vaginal delivery, say the authors.

They suggest that a significant reduction in neonatal respiratory morbidity may be obtained if elective caesarean section is postponed until 39 completed weeks of gestation.

Source: British Medical Journal