RANCHO MIRAGE, CALIF. — Women who had delivered vaginally were more than twice as likely to report stress urinary incontinence as were women who had delivered only by cesarean section in a study of 271 sets of identical twin sisters.
In a longstanding debate about the relationship of obstetric delivery mode and subsequent urinary incontinence, difficulty separating genetic from environmental factors has confounded study results. This study is the first on the subject with good control over the genetic factors, Roger P. Goldberg, M.D., said at the annual meeting of the Society of Gynecologic Surgeons.
Surveys completed by 542 women at the world's largest annual gathering of twins in 2003 and 2004 showed that 52% reported stress urinary incontinence.
Twelve percent of the women had more than five episodes of stress urinary incontinence per week.
Among all pairs of sisters, nulliparous women were the least likely to have stress incontinence, and having more than two births conferred nearly a fivefold increased risk of incontinence, compared with nulliparous women. With increasing numbers of vaginal births, the incontinence rate rose as high as 66%, said Dr. Goldberg of Northwestern University, Chicago, and his associates.
Higher body mass index (BMI) also was a risk factor for incontinence.
A second regression analysis of 196 sisters who were parous found that delivery mode was the major factor determining the risk of stress urinary incontinence, with vaginal birth doubling the chance of incontinence. “Parity and BMI were washed out by the effect of birth mode,” he said.
In this second analysis, 87% had at least one vaginal birth, and the rest delivered by cesarean only. The cesarean-only group had approximately half the rate of stress incontinence as did the vaginal birth group after the investigators controlled for age and BMI.
A final analysis that looked at 146 sisters who all had had at least one vaginal birth found that no factors specific to vaginal birth (such as forceps delivery) were significantly associated with incontinence.
The women had a mean age of 47 years. Among these relatively young, childbearing women, delivery mode “was the only modifiable risk factor for stress urinary incontinence that we were able to identify,” Dr. Goldberg said.
A separate study presented in poster format at the meeting found that insulin-requiring diabetes mellitus was independently associated with severe urinary incontinence in women aged 50–90 years, independent of other risk factors including patient age, BMI, and medical comorbidities.
Incontinence was not associated with diabetes that did not require insulin, reported Cynthia Lewis, M.D., of the University of New Mexico, Albuquerque, and her associates.
The study of 10,678 community-based women used self-reported data from the Health and Retirement Study, a large probability sample of U.S. households.
Severe incontinence was defined as losing urine on more than 15 days per month.
Overall, 22% of women reported some urinary incontinence, with 43% of that being severe incontinence.
The presence of insulin-requiring diabetes increased the risk for severe urinary incontinence by 63%, compared with nondiabetic women.
Among women with insulin-requiring diabetes mellitus, racial and ethnic minorities were less likely than were non-Hispanic white women to have urinary incontinence, Dr. Lewis said.
Mild incontinence (defined as leaking urine no more than five times per week) was associated with increasing BMI, hypertension, stroke, and arthritis, but not with diabetes, she added.