Introduction and Hypothesis
To compare hypotheses regarding why obesity is associated with stress
urinary incontinence (SUI): 1) obesity increases demands on the continence
system (e.g. higher cough pressure) vs 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 demands (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 between BMI, SUI, maximal cough pressure, MUCP, and POP-Q
point Aa.
Results
108 continent controls and 103 stress-incontinent women were
included. MUCP was the factor most strongly associated with SUI for all BMI
groups. Maximal cough pressure was significantly associated with SUI for
obese women (OR 3.191 (1.326, 7.683), p<.01), but not for normal or
overweight women. Path model analyses showed a significant relationship
between BMI and SUI through maximal cough pressure (indirect effect,
p=.038), but not through MUCP (indirect effect, p=.243) or
POP-Q point Aa (indirect effect, p=.410).
Conclusions
Our results support the first hypothesis: obesity is associated with
SUI because of increased intravesical pressure, which therefore increases
demand on the continence mechanism.