Structural and functional ultrasound imaging of the pelvic floor during pregnancy and postpartum

Abstract

This thesis focussed on the composition and functionality of the puborectalis muscle based on calculating echogenicity and strain from transperineal ultrasound recordings. It is its specific orientation that allows the levator ani muscle to lift (vertically in the standing posture) the pelvic organs and close the levator hiatus (horizontally in standing posture). Dysfunction of the pelvic floor muscles can be caused by instant trauma or long term deterioration. The most frequently reported risk factors for developing incontinence and pelvic organ prolapse are: pregnancy, mode of delivery, parity and Body-Mass-Index. The fact that the puborectalis muscle can be visualized on ultrasound images allows clinicians and researchers to study composition and function. In recent years three-dimensional (3D) and four-dimensional (4D) volume transperineal ultrasound imaging has become increasingly popular to study pelvic floor anatomy. Although measuring dimensions of the pelvic floor is well developed, identifying structural changes in the puborectalis muscle, apart from levator avulsions, is still in its infancy. We described the development of a semi-automated method to assess puborectalis muscle echogenicity on three-dimensional/four-dimensional (3D/4D) volume transperineal ultrasound images using 4D View and Matlab® software and evaluate its intra- and interobserver reliability. Echogenicity and area measurements of the puborectalis muscle can be performed reliably, and appears a promising new tool for studying pelvic floor structural anatomy. We evaluated the association between mean echogenicity of the puborectalis muscle, measured using transperineal ultrasonography, in women during their first pregnancy and the subsequent mode of delivery. The mode of delivery was classified into five categories: spontaneous vaginal delivery, instrumental vaginal delivery, elective cesarean delivery, cesarean delivery due to non-reassuring fetal status and cesarean delivery due to failure to progress. Of the 254 women included 157 had a spontaneous vaginal delivery, 47 underwent a cesarean delivery (11 elective, 36 emergency) and 45 had a vacuum operative vaginal delivery and in 5 patient files the mode of delivery was not recorded. Women who delivered by cesarean because of failure to progress had a significantly lower mean echogenicity of the puborectalis muscle on pelvic floor contraction at 12 weeks of gestation (116 ± 14) than women who had a spontaneous vaginal delivery (132 ± 21; Tukey's post-hoc test, p = 0.03), instrumental vaginal delivery (138 ± 21; p= 0.004) and cesarean delivery due to non-reassuring fetal status (139 ± 20; p= 0.02).The significantly lower mean echogenicity in women who had an emergency cesarean section due to failure to progress may be an indication of a disturbed early adaptation of this collagen metabolism, with less collagen being formed. We described the global strain of the puborectalis muscle during and after pregnancy. After delineation of the muscle on ultrasound images, the length of the midline of the puborectalis muscle was measured in the rest and contraction and global strain was expressed as percentile difference. After spontaneous and operative vaginal delivery the global strain significantly diminished as compared to pregnancy values. This did not occur in women who had a cesarean delivery. Vaginal childbirth thus negatively influences the strain of the puborectalis muscle.