Dr. Steven Swift, director of urogynecology and incontinence at the Medical University of South Carolina in Charleston, who did not participate in this research, said he wasn't surprised by the findings.

"Anybody who has ever witnessed a vaginal delivery realizes the baby's head is quite large and the muscles that it passes through are not that large. And any time you stretch a muscle there's the potential for damage," he told Reuters Health.

Incontinence, or leaking urine, can occur when the muscles supporting the urethra don't squeeze properly.

Although some doctors have assumed that vaginal birth puts women at higher risk of incontinence later on, studies haven't focused on the long-term effects of delivery methods.

Dr. Ian Milsom at the Sahlgrenska Academy at Gothenburg University in Sweden and his colleagues collected information on more than 5,200 mothers who had given birth once.

Their babies were all born between 1985 and 1988. About 1,200 were delivered via C-section and the rest vaginally.

When mothers were surveyed roughly 22 years after giving birth, 40 percent of those who'd had their babies vaginally said they experienced urine leakage. That compared to 29 percent of women who'd had a C-section.

Milsom said it appears that it's the last stages of vaginal delivery -- passing the baby through the birth canal -- that are important for later incontinence risk.

That's because women who began labor with the intention of delivering vaginally, but ended up getting a C-section, were just as likely to report incontinence 20 years later as women who planned their C-section.

The researchers calculated that doctors would have to perform eight or nine C-sections to avoid one case of long-term incontinence in moms.

While leaky urine can be bothersome, Milsom said future incontinence risk is not a reason to perform a C-section.

"We're not advocating doing cesarean sections on everybody," he told Reuters Health.

C-sections also come with potential risks such as breathing problems for babies and future pregnancy complications for moms.

Something that women can do to reduce their risk of incontinence is to control their weight, Milsom said.

His group found that among moms who'd had a C-section, obese women were more than three times as likely to have incontinence as normal-weight women. And obese mothers who'd delivered vaginally were two and a half times as likely to be incontinent as those who were normal weight at the time of the survey.

"This paper shows, most importantly to me, that if you control your weight you're going to do a lot better to control incontinence down the road than if you had a cesarean section over a vaginal delivery," Swift said.

He said one important measure missing from the study was how severe incontinence was.

For some women, occasional urine leakage is nothing to complain about. But for others, incontinence can be extremely disruptive.

"If you ask 100 women, 'Do you leak urine?' a lot of them will say, 'Yes.' The question is, how much does it bother you?" he said.

Milsom's results did show that women who had given birth vaginally were nearly three times as likely to have experienced incontinence for longer than a decade.

The authors of the study write in their report, published in BJOG: An International Journal of Obstetrics and Gynaecology, that the link between body size and incontinence is encouraging, "as it means that it is never too late to achieve an improvement of (urinary incontinence) through weight reduction and weight control."

SOURCE: bit.ly/yRSGJw BJOG: An International Journal of Obstetrics and Gynaecology, online March 14, 2012.

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