Women who deliver babies through Caesarean section are less likely than those who give birth vaginally to develop bladder control problems later in life, according to a large new study.

Twenty-one percent of women who gave birth vaginally developed incontinence, compared with 16 percent of women who had Caesareans and 10 percent among women who never had children, the study found.

The study, the largest to examine the issue, involved 15,307 Norwegian women who answered detailed questions about bladder control.

"These results suggest that the mechanical strain during labor may add to the risk associated with pregnancy itself," Gurt Rortveit, of the University of Bergen in Norway, and her colleagues wrote in today's issue of the New England Journal of Medicine.

"Although these results have relevance for policy regarding indications for cesarean sections, they should not be used as an argument for the increased use of cesarean."

In a telephone interview, Rortveit said that although the risk for incontinence is elevated among those giving birth vaginally, it is not high enough to justify the risks for the mother and child involved in a Caesarean, which is a major procedure in which a baby is removed surgically.

"To prevent one incidence of urinary incontinence, 13 women would have to have all their children by Caesarean sections," Rortveit said.

In recent years, more doctors have been advocating giving women the option to undergo a Caesarean, even if there is no obvious danger to her or the baby if a vaginal delivery were attempted.

One of the arguments has been that women who go through vaginal deliveries are more prone to health problems later in life as a result of damage that occurs to their bodies during labor and childbirth. They include nerve and muscle damage that can cause incontinence.

The findings are unlikely to settle the debate about Caesareans, which have reached an all-time high in the United States after declining for many years. The U.S. Caesarean section rate jumped 7 percent in 2001, reaching 24.4 percent of all live births -- the highest rate since the government started collecting the statistics, in 1989.

Opponents of elective Caesareans say they are more expensive and subject women to potentially dangerous surgery, which takes much longer to recover from.

In an article accompanying the study, Howard Minkoff of the Maimonides Medical Center and Frank A. Chervenak of Weill Medical College of Cornell University in New York wrote that while the findings "do not support the routine recommendation of elective cesarean section, we believe that it does support a physician's decision to accede to an informed patient's request for such a delivery."