The findings, from an American study of five million expectant mothers, will increase the debate about the rising Caesarean rate. More than one in five babies is born by c-section.
The study, the largest of its kind, looked at the risks of pregnant women developing placenta praevia, a condition in which the placenta covers the cervix, and placental abruption, when it becomes detached from the womb. Both conditions lead to bleeding, putting the lives of mother and baby at risk.
Researchers found that women who had a Caesarean section when they gave birth for the first time were 47% more likely to develop placenta praevia and 40% more likely to have placental abruption the next time they became pregnant.
They could not say for certain why, but believe the procedure caused scarring in the womb, which could affect the placenta’s ability to attach itself to the uterus properly.
A doctor may advise a Caesarean if a woman has a breech baby, if the baby is too big or its head is too high. A minority of women, so-called “too posh to push” mothers, choose to have the operation because they are worried about the pain of labour, the risks of incontinence after birth or believe it would be better for their sex life.
Prof James Walker, of St James’s University Hospital in Leeds, said he hoped the findings would encourage doctors to balance the risk of Caesarean sections before they decide against a natural birth.