Cross-sectional Area of Pubovisceral Muscle in Nulliparous and Primiparous Women

Pelvic-floor disorders (PFD), including pelvic organ prolapse, urinary and fecal incontinence, decrease quality of life of every fourth women. 1 The main known risk factor for PFD is vaginal delivery 2,3 causing pelvic floor muscle avulsion, ischemia or denervation.4 Ultrasound (US) and magnetic resonance imaging (MRI) are frequently used to investigate structural changes in pelvic floor muscles. The investigators aimed to focus on structural changes (atrophy) caused by muscle denervation. 5 The pubovisceral muscle (PVM) is the part of the levator ani muscle (LAM) which is most frequently injured and it is thought to be possibly denervated by overstretching 6 Recently, the most precise measurement of PVM cross-sectional area was performed by the group of DeLancey. 7 In our study, the investigators aimed to describe which are the normal values of PVM volume in nulliparous women. The investigators performed a measurement of PVM volume in women after the first vaginal delivery. The investigators hypothesized that there will be a decrease of the cross-sectional area of the PVM developed after denervation trauma.

Two groups of women were recruited. First, the nulliparous group served as a control. The second group was women after their first vaginal delivery. Personal characteristics, anamnestic and delivery data were collected, and clinical examination, ultrasound (US) and magnetic resonance imaging (MRI) was performed. The number of women to reach significance in the study was 40/per group. The investigators did not expect a transfer of patients between the two groups. Volunteers were recruited from a general gynecological outpatient clinic. They were thoroughly informed and informed consent was provided. In nulliparous women, all examinations (clinical, US, MRI) were performed only once. In women after vaginal delivery, first US was performed within 72h after childbirth, in order to detect LAM avulsion and exclude these women. In women without avulsion, 6 weeks after delivery, during a general postpartum checkup, the clinical evaluation of pelvic floor muscle contraction was performed. In those where the score is 0-3 the 3D US was performed to confirm no change of hiatal area during contraction. Those scans were recorded as investigated data. Those women underwent MRI within 4 months US images were obtained with a GE Voluson E10 system (General Electric Healthcare, Chicago, IL) by one investigator. US data acquisition was performed translabial as already described.9 Volumes were acquired at rest, during Valsalva and contraction. From acquired volume was assessed PVM avulsion, size of urogenital hiatus. Decrease of hiatal area at contraction proves muscle function. The assessment of US scans was performed off-line at axial plane using the 4D View v 2.1-5.0 software (GE Medical Systems) by two investigators blinded against all clinical data. MRI images were obtained with a 3-T scanner (AchievaTM, Philips Healthcare). MRI included coronal, axial, and sagittal proton density-weighted sequences performed at rest, Valsalva and contraction. Primary outcome evaluated by MRI will be the cross-sectional area of the PVM. The precise MRI technique was already defined by the group of DeLancey and is in detail described in recent publication.7 Evaluation was performed off-line by two investigators blinded against all clinical data using ImageJ software. Intra- and interobserver variability was calculated.