DELIVERY MODE IS A MAJOR DETERMINANT OF STRESS URINARY INCONTINENCE IN CHILDBEARING WOMEN:  ANALYSIS OF 542 IDENTICAL TWINS

R.P. Goldberg, Y. Abramov, S. Botros, J. Miller, M. Rurak, P. Sand

Evanston Continence Center, Evanston, IL; Northwestern University, Feinberg School of Medicine, Chicago, IL

OBJECTIVE:  The relationship between obstetrical delivery mode and SUI has been a subject of longstanding debate. We administered an extensive survey of incontinence symptoms to a large sample of identical twin sisters, to determine the main environmental determinants of SUI and explore the impact of delivery mode.  Identical twin studies are regarded as an ideal methodology for assessing environmental disease factors, providing ‘natural control’ over genetic variance that cannot be achieved within random samples of unrelated individuals.

MATERIALS AND METHODS: The anonymous 67-item survey was completed by 271 identical twin sister pairs (n=542) at the world’s largest annual gathering of twins in 2003 and 2004.  Logistic regression for repeated binary measures was used to account for correlated data between pairs.  Three models were utilized: (A) all pairs including those with nulliparous women (n=288), (B) pairs for which both sisters gave birth by either vaginal or cesarean mode (n=196), and (C) pairs for which both sisters specifically had at least one prior vaginal birth (n=146).  This facilitated evaluation of all demographic, environmental and obstetrical factors while maintaining valid reference groups.

RESULTS: Demographics included mean age 47.1 (15-85), parity 2 (0-7), 45% menopausal, mean BMI 26.4, 90.3% Caucasian and 6.7% African American.  SUI was reported by 51.8%; 87.4% had 1-5 weekly episodes, 12.2% had >5.  Among parous women, 87.3% reported at least one vaginal birth and 12.7% had cesarean only; SUI rates for these groups were 67.1% and 47.7%, respectively. Regression Model A confirmed associations between SUI and age (OR 2.3 for age >40; OR 2.8 for age >60, p=0.001), parity (OR 2.3 for 1 birth; OR 4.3 for >2 p=0.001), and BMI>30 (OR 3.4, p=0.001). Model B assessed the impact of obstetrical factors and birth mode, in parous-parous twin pairs.  This model revealed delivery mode as independently predictive of SUI, with ‘cesarean only’ conferring a substantial reduction in SUI risk relative to vaginal birth (OR 0.43, p=0.01) after controlling for parity and BMI.  Non-significant factors included prolonged 2nd stage and newborn weight.   Model C evaluated factors specific to vaginal birth mode, revealing trends between SUI and macrosomia (OR 1.7, p=0.07) and forceps (OR 1.8, p=0.16).  Episiotomy demonstrated no relationship to SUI (OR 1.01, p=0.42).

CONCLUSIONS:  This study of SUI in identical twin sisters is the first to provide nearly complete control over genetic factors (‘nature’) that typically confound the evaluation of environmental and obstetrical factors (‘nurture’).  Delivery mode and obesity appear to be the most potent environmental determinants of SUI among younger childbearing women, with vaginal childbirth conferring a markedly higher risk of SUI than cesarean (OR=2.32, p=0.01).  These findings highlight the impact of obstetrical choices on post-reproductive urinary function.

Key Words:  stress incontinence, childbirth, epidemiology, risk factors 

Disclosure – Speakers Bureau: P.K. Sand, Alza/Ortho-McNeil, Watson, American Medical Systems; Advisory Board: P.K. Sand, Alza/Ortho-McNeil, Watson, American Medical Systems, Indevus, Yamanouchi, Roche, Pfizer, Bioform, Lilly, Boeringer-Ingelheim, Mentor, Novasys; Grant/Research: P.K. Sand, Alza/Ortho-McNeil, Watson, American Medical Systems, Indevus, Yamanouchi, Roche, Pfizer, Bioform, Lilly, Boeringer-Ingelheim, Mentor, Novasys.