Changes in Morphology of the Urethral Rhabdosphincter Postpartum

The aim of the study was to determine the effect of pregnancy on urethral rhabdosphincter cross-sectional area (CSA) and any association of CSA to urinary symptoms.

Nulliparous women planning pregnancy (N = 135) underwent standardized evaluations (symptom and quality of life [QOL] questionnaires, magnetic resonance imaging, ultrasonography, and neurophysiologic testing) between January 2008 and December 2013 (V1). The participants who became pregnant and gave birth underwent the same evaluations at 6 weeks (V2) and 6 months postpartum (V3). Participants who had magnetic resonance imaging data from both V1 and V3 were selected. We measured urethral rhabdosphincter CSA from high-resolution axial MRIs in a masked fashion. The mean CSA for each participant was calculated. The change from V1 to V3 was assessed.

Sixty-eight women were evaluated. There was a significant decrease of 0.05 cm2 (interquartile range, -0.03 to 0.16 cm2; P = 0.002) in the median sphincter CSA between V1 and V3. There was a significant increase in the median Urinary Distress Inventory (UDI) subscore of the Pelvic Floor Distress Inventory (PFDI) from V1 to V3 (median increase of 0 [IQR, 0 to 8.3]; P = 0.033), but this was not significantly correlated with the change in the urethral CSA (Spearman correlation, 0.199; P = 0.107). Increasing fetal weight was correlated with a decrease in CSA postpartum after vaginal birth (Spearman correlation, -0.340; P = 0.017).

There is a decrease in urethral rhabdosphincter CSA with worsening Urinary Distress Inventory scores from prepregnancy to postpartum, but these two do not correlate in this cohort with low symptom levels. Among women who give birth vaginally, decrease in rhabdosphincter CSA is correlated with increasing fetal weight, perhaps with ramifications to be seen later in life.