Two new studies reach somewhat different conclusions about whether women who deliver vaginally are more likely to develop bladder control problems than women who deliver by C-section.
Concern about urinary incontinence is thought to be one reason for the trend of women who probably could deliver vaginally opting for a cesarean.
Doctors have long considered childbirth the main risk factor for incontinence, says University of Rochester urogynecologist Gunhilde Buchsbaum, the lead author of one of the studies. It is published in the December issue of Obstetrics & Gynecology.
Buchsbaum's study suggests that genetics, not childbirth, determines whether a woman will become incontinent. Her results appear to be at odds with a study in the December issue of the American Journal of Obstetrics and Gynecology, which found that women who delivered vaginally were more than twice as likely to report urinary incontinence as women who had only C-sections.
Buchsbaum and her co-authors studied 143 pairs of postmenopausal sisters whose average age was 61. In each pair, one sister had given birth vaginally, on average, three times. The other had never delivered a baby.
About 50% of those who had given birth reported urinary incontinence, compared with about 48% of those who had not, a difference too small to be statistically significant, the researchers write. But in 63% of the pairs, both sisters were either continent or incontinent, highlighting the role of genetics.
"This isn't 100% definitive, but it's about as definitive as you can get on this issue," says co-author David Guzick, dean of the University of Rochester School of Medicine and Dentistry.
So how to explain the other new study, which found an increased risk of incontinence in women who had had a C-section?
Age might be a factor. Roger Goldberg and co-authors surveyed 271 pairs of identical twins whose average age was 47 -- considerably younger than the women in Buchsbaum's study. A little more than half were premenopausal. By focusing on identical twins, "you totally eliminate any possibility that any differences you find are due to genetics," says Goldberg, director of urogynecology research at Evanston-Northwestern Healthcare in Evanston, Ill.
Mode of delivery "is a major factor for women in their younger years," Goldberg says. But, as Buchsbaum's research and that of others suggest, the impact of mode of delivery on incontinence risk disappears by menopause.
Goldberg says his findings do not suggest that doctors should recommend cesareans just to prevent incontinence, although, "it's part of what women need to know."
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