Vaginal birth is a risk factor for developing urinary incontinence [1] due to birth-related injuries. Pubovisceral muscle tear is one common birth-related injury that often occurs on the pubovisceral portion of levator ani among postpartum women with high risk factors for the tear during birth [2]. Continence relies on optimization of urethral closure pressure across women’s activities. Pelvic muscle contraction to preempt leakage (e.g. during cough) has been shown to be effective [3]. However, little is known about the degree to which pubovisceral muscle tear affects potential for urethral closure pressure with a volitional pelvic muscle contraction. To investigate the effect of pubovisceral muscle tear on ability to increase urethral closure pressure by a volitional pelvic muscle contraction among women within the first year post vaginal birth who have known risk factors for pubovisceral muscle tear during that birth (e.g. forceps, long 2nd stage, and older age).

Fifty-six primiparas were evaluated at about 8 months postpartum in this secondary data analysis study. Urethral closure pressures were measured by urethral pressure profile both at rest, which is called resting urethral closure pressure and during effort to contract the pelvic muscle, which is volitionally contracting urethral closure pressure. Pubovisceral muscle tear was evaluated by magnetic resonance imaging (MRI) and was classified into one of five categories from none to >50% tear for each side. We coded MRI-documented pubovisceral muscle tear status into a dummy variable as 0 (without tear) and 1 (with tear) for two sides for simplicity of presenting the data via multiple linear regression modeling. We tested whether pubovisceral muscle tear predicts contracting urethral closure pressure after adjusting for resting urethral closure pressure.

There was no significant difference in resting urethral closure pressure between no pubovisceral muscle tear and tear groups (Table 1). Women without tear had higher contracting urethral closure pressure compared to those with tear (Table 1). Women with tear could not significantly increase contracting urethral closure pressure. Multiple regression modeling showed that the contracting urethral closure pressure was associated with the pubovisceral muscle tear (p = .001), after adjusting for resting urethral closure pressure (p < .001), with unstandardized coefficient 21 centimeters of water for pubovisceral muscle tear and coefficient of determination R square = .42 (Table 2).

A MRI-documented pubovisceral muscle tear decreases mean contracting urethral closure pressure by on average 21 centimeters of water pressure, when controlling for the resting urethral closure pressure constant. R square = .42 from the regression model indicated that 42% of the variation in the contracting urethral closure pressure was explained by pubovisceral muscle tear and resting urethral closure pressure. With pubovisceral muscle tear, women on average have reduced ability to increase contracting urethral closure pressure at a moment of anticipated increased bladder pressure, as with sneeze or cough.

Within the first year of vaginal birth, women with pubovisceral muscle tear are significantly less able to increase urethral closure pressure by using a volitional pelvic muscle contraction. Since lifetime continence requires adequate urethral closure pressure, pubovisceral muscle tear may explain the reduced ability to compensate for known age-related loss of urethral closure pressure over time.

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