Thousands of women give birth by caesarean each year

Doctors say the finding, published in the Lancet medical journal, could dissuade women who want caesareans despite having no clear medical reason.

The Cambridge University team looked at 120,000 births to find the difference in stillbirth rate.

However, even if raised, the overall risk of a stillbirth remains small - just 2.4 per 10,000 births.

More than a fifth of all babies born in England are delivered by caesarean section, where a surgeon cuts into the womb to take out the child.

Three out of five of these are emergency caesareans, and many of the others are planned because doctors have spotted complications which mean natural birth could put her or her baby at risk.

Mother's choice

However, up to 7% of caesareans are chosen by the mother even though no there are no complications, and doctors think she could quite safely give birth naturally.

It is already known that caesareans are linked to an increased rate of placental problems in subsequent pregnancies, but there has been no clue as to whether there is any possibility of harm to the foetus.

The rate of stillbirth of a subsequent child among women who had already had one child naturally is approximately 1.4 per 10,000 births.

The rate for women who had had a caesarean - regardless of the reason for it - was 2.4 per 10,000 births.

There was no obvious reason for the increase - such as the medical reason which led to a first caesarean influencing the outcome of subsequent pregnancies.

No advantage

Professor Gordon Smith, who led the study, said that in situations where there was a potential risk to the baby, these findings were not likely to persuade a mother to reject a caesarean.

He said: "The overall excess risk of stillbirth in a second pregnancy that was associated with a previous caesarean delivery was below one per 1,000, which is unlikely to influence the decision to have a caesarean for breech presentation in the first pregnancy.

"However, if women are being counselled about caesarean birth with no clear obstetric advantage, such as caesarean section for maternal request, the possible effect on the risk of unexplained stillbirth on future pregnancies should be discussed."

Dr Judith Lumley, from the Centre for the Study of Mothers' and Children's Health in Victoria, Australia, said that the study should encourage doctors at maternity hospitals to reassess how many caesareans they carry out.

"The implication might be that maternity hospitals where caesarean first births are commoner than in other local settings need to think more seriously about strategies for reducing the number of caesarean sections."