Women who try to give birth naturally after having had a Caesarean face a slightly higher risk of serious medical problems, according to a comprehensive study released on Tuesday.

The finding, based on the cases of more than 33,000 women and scheduled to be published in Thursday’s New England Journal of Medicine, may help settle a decades-old debate.

Doctors used to think a woman who had delivered one baby via a Caesarean section should have all subsequent deliveries the same way.

That belief was one reason surgical deliveries eventually represented more than a quarter of all births. In 1981, only 3 percent of such women tried conventional labor if they became pregnant again.

Because any surgery, including Caesarean, poses risks, doctors tried to bring that rate down by giving women a chance to deliver vaginally before resorting to a C-section. By 1996, 28 percent of those women were having conventional deliveries.

But that, in turn, seemed to produce more cases where the scar tissue of the uterus tore during labor - a serious complication. That helped the pendulum swing back. By 2002, fewer than 13 percent of such women were having their babies vaginally.

The new study, led by Mark Landon of Ohio State University and based on data from 19 U.S. medical centers, was designed to better assess the risks.

The Landon team found that 0.7 percent of women who had previously delivered by Caesarean section had their uterus rupture when they tried to deliver naturally.

And while no babies delivered surgically suffered from lack of oxygen, there were 12 such cases among mothers who attempted a vaginal delivery. Two of the 12 babies died.

The risk of death for the mother was the same for the two groups of women.

The risks may be higher for women who attempt a vaginal delivery “although the absolute risks are low,” the researchers concluded.

Landon and his colleagues also discovered that the risk of uterine rupture increased to 1.1 percent from 0.7 percent when the drug oxytocin was used to induce labor.

The study found that 588 Caesarean deliveries would need to be done to prevent one serious problem among women who first tried to deliver vaginally.

In an editorial in the Journal, Michael Green of Massachusetts General Hospital said some women and their doctors might perceive the danger of trying a vaginal delivery to be small, while others may disagree.

“Ultimately,” he said, “risk, like beauty, is in the eye of the beholder.”