Obesity and stress urinary incontinence in women: compromised continence mechanism or excess bladder pressure during cough?
OBJECTIVE
We compared two hypotheses as to why obesity is associated with stress urinary incontinence (SUI): (1) obesity increases demand on the continence system (e.g. higher cough pressure) and (2) obesity compromises urethral function and urethrovaginal support.


METHODS
A secondary analysis was performed using data from a case-control study of SUI in women. Measurements of urethrovaginal support (POP-Q point Aa, urethral axis), urethral function (maximal urethral closure pressure, MUCP), and measures of continence system demand (intravesical pressures at rest and during maximal cough) were analyzed. Cases and controls were divided into three body mass index (BMI) groups: normal (18.5-24.9 kg/m2); overweight (25.0-29.9 kg/m2); and obese (≥30 kg/m2). Logistic regression models where created to investigate variables related to SUI for each BMI group. Structural equation modeling was used to test the direct and indirect relationships among BMI, SUI, maximal cough pressure, MUCP, and POP-Q point Aa.


RESULTS
The study included 108 continent controls and 103 women with SUI. MUCP was the factor most strongly associated with SUI in all BMI groups. Maximal cough pressure was significantly associated with SUI in obese women (OR 3.191, 95% CI 1.326, 7.683; p < 0.01), but not in normal weight or overweight women. Path model analysis showed a significant relationship between BMI and SUI through maximal cough pressure (indirect effect, p = 0.038), but not through MUCP (indirect effect, p = 0.243) or POP-Q point Aa (indirect effect, p = 0.410).


CONCLUSIONS
Our results support the first hypothesis that obesity is associated with SUI because of increased intravesical pressure, which therefore increases demand on the continence mechanism.
Department of Obstetrics and Gynecology, L4000 Women's Hospital, University of Michigan, 1500 E. Medical Center Dr., SPC 5276, Ann Arbor, MI, 48109-5276, USA. scarolyn@med.umich.edu.
Carolyn W
CW
Swenson
Department of Obstetrics and Gynecology, L4000 Women's Hospital, University of Michigan, 1500 E. Medical Center Dr., SPC 5276, Ann Arbor, MI, 48109-5276, USA.
Giselle E
GE
Kolenic
University of Virginia, Charlottesville, VA, USA.
Elisa R
ER
Trowbridge
Department of Obstetrics and Gynecology, L4000 Women's Hospital, University of Michigan, 1500 E. Medical Center Dr., SPC 5276, Ann Arbor, MI, 48109-5276, USA.
Mitchell B
MB
Berger
Northwestern University, Chicago, IL, USA.
Christina
C
Lewicky-Gaupp
Kaiser Permanente, Oakland, CA, USA.
Rebecca U
RU
Margulies
Department of Obstetrics and Gynecology, L4000 Women's Hospital, University of Michigan, 1500 E. Medical Center Dr., SPC 5276, Ann Arbor, MI, 48109-5276, USA.
Daniel M
DM
Morgan
Department of Obstetrics and Gynecology, L4000 Women's Hospital, University of Michigan, 1500 E. Medical Center Dr., SPC 5276, Ann Arbor, MI, 48109-5276, USA.
Dee E
DE
Fenner
Department of Obstetrics and Gynecology, L4000 Women's Hospital, University of Michigan, 1500 E. Medical Center Dr., SPC 5276, Ann Arbor, MI, 48109-5276, USA.
John O
JO
DeLancey
D000328:Adult; D015992:Body Mass Index; D016022:Case-Control Studies; D003371:Cough / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008875:Middle Aged; D009765:Obesity / Q000150:complications* / Q000503:physiopathology*; D011312:Pressure; D001743:Urinary Bladder / Q000503:physiopathology; D014550:Urinary Incontinence, Stress / Q000209:etiology*; D014563:Urodynamics / Q000502:physiology
Obesity; Pelvic floor disorders; Urinary stress incontinence; Urodynamics