They face a slightly higher risk of serious medical problems, including tearing of the womb, Ohio State University researchers conclude.

Their findings are based on 46,000 women and appear in the New England Journal of Medicine.

One in five births in England and Wales are by Caesarean section.

An audit of 3,000 women by the Royal College of Obstetricians and Gynaecologists in 2001 showed two-thirds of these were carried out as emergency procedures and the other third were opted for electively.

Of those women who went on to have another child, a third opted to attempt a natural vaginal delivery.

The National Institute for Clinical Excellence advises doctors that pregnant women who have had a previous Caesarean and who want to have a vaginal birth should be supported in this decision.

But it also points out that the overall risks and benefits of caesarean should be discussed with the woman.

The risks

The NEJM study found the risk of uterine rupture was less than 1% among women who opted to try a natural delivery after having had a Caesarean in the past, compared to women opting for another Caesarean.

The overall risk for a serious complication for the newborn baby was about one in 2,000.

The benefits of a natural birth include a faster recovery and a shorter hospital stay as well as avoiding the risks of major surgery, said the researchers.

Of the 46,000 women included in the study, about 16,000 chose to undergo a repeat Caesarean delivery, 12,000 had to have a Caesarean for medical reasons and 18,000 attempted a vaginal birth - 73% successfully.

Lead researcher Dr Mark Landon said: "While the magnitude of these risks for serious complications is small, women who have had a previous Caesarean section and who are considering choices for childbirth should be aware of the level of risk involved.

"Many women will continue to opt for an attempt at vaginal birth after Caesarean," he said.

Mary Newburn, head of policy research at the National Childbirth Trust, said: "There is currently a considerable body of research evidence on vaginal birth after Caesarean, though the full range of risks and benefits compared with a repeat Caesarean section, are still uncertain.

"This latest research confirms that absolute risks are low.

"Women should be given information about the health implications of different kinds of care and different ways of giving birth, so that they can make informed decisions."

Dr Alan Cameron, consultant obstetrician at the Queen Mother's Hospital in Glasgow, said: "We do take it seriously.

"If women have had a previous Caesarean we will council them that that is a major operation and there are risks to undergo labour but there are risks having a planned Caesarean section too.