Babies delivered by planned Caesarean section are up to four times more likely to have breathing problems than those born naturally, a large study suggests.

The earlier the procedure is done, the greater the risk, with up to one in ten infants suffering complications if they are delivered at 37 weeks’ gestation. The finding adds to the evidence about the risks of Caesareans, which are increasing in Britain, now accounting for nearly a quarter of births. The World Health Organisation recommends a rate of 10 to 15 per cent.

Although there can be valid medical reasons for a Caesarean, experts have called for measures to reduce the number of women having the operation when they could deliver normally.

The new study, published on the British Medical Journal website, found that babies delivered by planned Caesarean section were also far more likely to suffer breathing difficulties than those delivered by emergency Caesarean.

The exact reasons are unknown, but it is suggested that hormonal and physiological changes associated with la-bour are necessary for the lungs to mature. How well-developed the baby is at the time of the operation may be a factor, the researchers said. They suggest that the severity of breathing difficulties can be reduced by waiting until at least 39 weeks to have a Caesarean.

Experts from Aarhus University Hospital in Denmark carried out the study of 34,458 babies born at between 37 and 41 weeks from 1998 to 2006. The study included 2,687 babies delivered by elective Caesarean section (7.8 per cent) and 2,877 by emergency Caesarean. Factors that could affect the results, such as the mother’s tobacco and alcohol intake, her body mass index, age and education, were also taken into account.

It was found that 2.8 per cent of infants delivered normally at 37 weeks had respiratory problems compared with 10 per cent of those delivered by elective Caesarean. At 38 weeks the proportion was 1.7 per cent compared with 5.1 per cent, and at 39 weeks 1.1 per cent compared with 2.1 per cent.

The authors wrote: “This study suggests that elective Caesarean section compared with intended vaginal delivery leads to a twofold to fourfold increased risk of overall neonatal respiratory morbidity and even higher relative risks of serious respiratory morbidity in term newborns. This information should be taken into consideration by women contemplating an elective Caesarean section and by the obstetricians counselling them.”

In emergencies, Caesareans save lives, but having the operation by choice has been associated with several problems. In October an Oxford University study found that women could be four times more likely to die in childbirth if they opted for a Caesarean instead of a natural birth. Another study found that the risk of a stillbirth in a second pregnancy can double if a woman previously had a Caesarean.

Other risks to the mother include bleeding and infection, while her baby is more likely to need specialist care.

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