Pelvic floor muscle variables and levator hiatus dimensions: a 3/4D transperineal ultrasound cross-sectional study on 300 nulliparous pregnant women

Abstract

Introduction and hypothesis: The aims of the present study were to investigate the correlation among vaginal resting pressure and pelvic floor muscle (PFM) strength and endurance, and the correlation between the same variables and levator hiatus (LH) dimensions in nulliparous pregnant women. Methods: This was a cross-sectional study of 300 nulliparous pregnant women, mean age 28.7 years (SD 4.3) and pre-pregnancy BMI 23.9 kg/m2 (SD 3.9), assessed at mean gestational week 20.8 (±1.4). Vaginal resting pressure and PFM strength and endurance were measured using a high precision pressure transducer connected to a vaginal balloon. LH dimensions (transverse and anterior–posterior diameters_ and LH area were assessed using 3/4D transperineal ultrasound in the axial plane of minimal hiatal dimensions using render mode. The Pearson correlation was used to analyze correlations among vaginal resting pressure and PFM strength and endurance, and between PFM variables and LH dimensions. Level of significance was set at 0.05. Results: Pelvic floor muscle strength and vaginal resting pressure were significantly, but weakly correlated (r = 0.198, p < 0.001). PFM strength and endurance showed a strong correlation (r = 0.929, p < 0.001). High vaginal resting pressure was moderately correlated with a small LH area at rest (r = −0.451, p < 0.001), but there was no significant correlation neither between PFM strength and LH area at rest (r = −0.012, p = 0.84) nor between muscle endurance and LH area at rest (r = −0.014, p = 0.81). A strong PFM contraction correlated moderately with reduction of the LH area (r = −0.367, p < 0.001). Conclusions: Pelvic floor muscle strength and endurance are strongly correlated, butdo not correlate with a smaller LH area at rest.