Methods
This is an observational retrospective study, consecutively screening primiparas who conducted the regular prenatal examinations and delivered between January 2019 and December 2020 at the International Peace Maternal and Child Health Hospital in Shanghai. This study was approved by the Medical Science Ethics Committee of the International Peace Maternal and Child Health Hospital.
Our study screened study subjects, who experienced singleton delivery as primipara, and whose neonates less than 4000g, who had cesarean section or vaginal delivery with / without perineum laceration limited in degree II. Meanwhile, we excluded the subjects who was younger than 18-year-old or older than 50-year-old; who had premature birth at fewer than 28 weeks gestational age; who conceive a fetus with known congenital anomalies; who had stillbirth; who had at moment vaginitis and pelvic inflammatory disease; who had chronic coughing and chronic constipation; who had other systemic comorbidities (e. g. heart, liver and kidney disease, hematological disease, respiratory disease, etc.).
In general, we set up two study groups, cesarean section delivery group (CD) and vaginal delivery group (VD), in order to analyze the impact of these two main modes of delivery on PFD. Furthermore, the vaginal delivery group were separated into four subgroups, including Group A with intact perineum or first-degree perineum laceration, Group B with second-degree perineum laceration, Group C with lateral episiotomy, as well as Group D with forceps delivery.
The clinical data of pregnancy and delivery were obtained from electronic medical records system. At 6–8 weeks postpartum, all subjects underwent the routine assessments, which included the inquiry of medical history, gynecological examination and the sEMG evaluation of the PFM function.
PFM function was evaluated with vaginal palpation and sEMG. All patients routinely were offered the instructions and information about sEMG before the examination, by a trained urogynecologist of the Pelvic Floor Diagnosis and Treatment Center. Participants were in supine position and requested to be relaxed in the whole process of the sEMG examination. During the process, the automated protocol software provided the participants real-time instruction by voice messages and figures on monitor, with which the participants could relax or contract the PFMs accordingly. The sEMG facility used in this study was a Biofeedback electrical stimulator made by Nanjing Mai Lan De Medical Technology, Ltd, Nanjing, China (mode: MLD A2). It has 2 channels, composed of Channel 1 to acquire the electromyographic signal by inserting an intravaginal sensor probe into the vaginal cavity; and Channel 2, to acquire the EMG signals from abdominal muscles by electrode patches attaching to the abdomen.
With the collected amplified the EMG signal, muscle fiber recruitment and relaxation time, muscle fiber type and fatigue, all these data were processed and presented visible interpreted curves on the computer interface by certain software. The combination of channel 1 and 2 were processed and analyzed the percentage of abdominal muscle engagement.
A modified Glazer protocol was used to analyze the pelvic floor sEMG value. The modified Glazer Protocol includes 4 activities, and the signal parameters were calculated for each activity.
1. The rest (pre-baseline) phase: the subjects were instructed to feel the pelvic floor muscle in rest remaining for 10-second. To test the PFM tension in a relaxed state.
Average Mean Amplitude (µV)
2. The phasic (flick) contraction phase: the subjects were instructed to quickly contract the PFM, and then fully relax the PFM immediately after contraction (five 2-second contraction with a 2-second rest in-between). To test muscle strength and reaction velocity of the fast muscle fibers (Class II fibers).
Average Peak Amplitude (µV): the mean value of 5 contractions
Time Before Peak (s): the mean value of 5 contractions
Time After Peak (s) - the mean value of 5 contractions
3. The tonic contraction phase:the subjects were instructed to contract the PFM as strongly as possible and hold the contraction for 10 seconds,then fully relax the PFM after contraction for 10 seconds. To test muscle strength and contractile stability of the slow muscle fibers (Class I fibers).
Average Mean Amplitude(µV) - the mean value of 5 contractions
Mean Amplitude Variability (%)
4. The rest (post-baseline) phase: the subjects were instructed to feel the PFM in rest for 10-second. To test the PFM tension in a relaxed state.
Average Mean Amplitude (µV)
All the relevant data were filled in Excel to establish a database. Statistical analysis was performed using SPSS 26.0. If the date showed normal distribution and the equal variance, the measurements presented as x±s and were analyzed by t-test for comparisons between two groups and one-way ANOVA for comparisons among multiple groups. Those data that did not meet a normal distribution or a equal variance, presented as the median [M (P25, P75)], the Mann-Whitney U-test was used for comparisons between two groups, while the Kruskal-Wallis rank sum test was used for comparisons among multiple independent samples. P<0.05 was considered statistically significant.