## 2 Materials and Methods
### Study Design  
All subjects gave their informed consent for inclusion before they participated in the study. The study was conducted in accordance with the Declaration of Helsinki, and the protocol was approved by the Ethics Committee of the Medical University of Lodz (RNN/321/18/KE). Every patient was familiarized with the Patient Information regarding participation in the study. Written informed consent was obtained from each participant prior to enrollment in the study. Three study visits were conducted for each participant. The visit V0 was for participant screening. The visit V1 was conducted on the same day as V0 or up to 7 days after. The visit V2 was conducted up to 21 days after V1. At V1, the inclusion/exclusion criteria were checked and the medical history with obstetrics and neonatology details were collected. The physical examination, including gynecological and proctological exams, were carried out. The presence of clinical symptoms of fecal incontinence was checked using the Wexner scale (0-20 points in 5 questions, where 0 means complete commence, and 20 means full incontinence). Then, the ONIRY Meter and ONIRY Probe were used to perform the impedance spectroscopy test. During visit V2, 3-dimensional endoanal ultrasound (to estimate the injury using the OASI classification, which assesses the problem in 4 degrees: 1 and 2 refers to perineal \begin{table}
\begin{tabular}{l c c} \hline \hline  & \(\mathbf{Wexner=0}\) & \(\mathbf{Wexner>0}\) \\ \hline Number of patients & 12 & 8 \\ Primiparous & 6 & 4 \\ Multiiparous & 6 & 4 \\ Age & 30.58 \(\pm\) 3.92 & 33.13 \(\pm\) 3.98 \\ Functional length of anal canal (mm) & 35.75 \(\pm\) 28.63 & 29.63 \(\pm\) 6.95 \\ OASI classification & 1.50 \(\pm\) 0.67 & 2.13 \(\pm\) 0.64 \\ Starck scale [51] & 0.25 \(\pm\) 0.87 & 2.13 \(\pm\) 5.62 \\ Norderval scale [52] & 0.08 \(\pm\) 0.29 & 1.00 \(\pm\) 2.45 \\ Max. sphincter contr. press. (cm\(H_{2}\)O) & 194.00 \(\pm\) 49.64 & 150.44 \(\pm\) 44.44 \\ Mean sphincter contr. press. (cm\(H_{2}\)O) & 148.92 \(\pm\) 36.78 & 118.81 \(\pm\) 34.14 \\ Resting rectal press. (cm\(H_{2}\)O) & 85.25 \(\pm\) 16.56 & 87.90 \(\pm\) 20.69 \\ Max. anal sphincter press. (cm\(H_{2}\)O) & 203.25 \(\pm\) 44.47 & 156.84 \(\pm\) 36.83 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Summary of baseline characteristics of the study group and anorectal manometry measurements broken down by Wexner scale [33]. Data are presented as a number of patients (N) or mean \(\pm\) standard deviation. All patients with a score above 2 in the OASI classification had a lesion scored as 3a, which was converted to 3 for the calculations. \begin{table}
\begin{tabular}{l c c} \hline \hline  & \(\mathbf{OASI\leq 2}\) & \(\mathbf{OASI>2}\) \\ \hline Number of patients & 17 & 3 \\ Primiparous & 8 & 2 \\ Multiparous & 9 & 1 \\ Age & 32.06 \(\pm\) 4.13 & 29.00 \(\pm\) 2.65 \\ Functional length of anal canal (mm) & 33.53 \(\pm\) 6.88 & 32.00 \(\pm\) 6.56 \\ OASI classification & 1.53 \(\pm\) 0.51 & 3.00 \(\pm\) 0.00 \\ Starck scale [51] & 0.00 \(\pm\) 0.00 & 6.67 \(\pm\) 8.14 \\ Norderval scale [52] & 0.00 \(\pm\) 0.00 & 3.00 \(\pm\) 3.46 \\ Max. sphincter contr. press. (cm\(H_{2}\)O) & 177.82 \(\pm\) 40.28 & 169.53 \(\pm\) 109.33 \\ Mean sphincter contr. press. (cm\(H_{2}\)O) & 139.92 \(\pm\) 33.62 & 119.63 \(\pm\) 64.31 \\ Resting rectal press. (cm\(H_{2}\)O) & 86.72 \(\pm\) 17.27 & 84.00 \(\pm\) 24.06 \\ Max. anal sphincter press. (cm\(H_{2}\)O) & 182.64 \(\pm\) 40.67 & 216.00 \(\pm\) 104.65 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Summary of baseline characteristics of the study group and anorectal manometry measurements broken down by OASI classification (\(\leq\)2 for Group A and \(>\)2 for Group B) [8]. Data are presented as a number of patients (N) or mean \(\pm\) standard deviation. All patients with a score above 2 in the OASI classification had a lesion scored as 3a, which was converted to 3 for the calculations.