Ethical approval
The study protocol was approved by the Ethics Committee of Maternal and Child Health Hospital of Hubei Province (201301) and all included women signed written informed consent.
Selection of patients and study design
Women who had delivered in the obstetric department and visited in the pelvic floor rehabilitation center in postpartum 6–8 weeks period at the Maternal and Child Health Hospital of Hubei Province, Tongji Medical College, Huazhong University of Science and Technology from January 2016 to January 2017 were selected as research objects. Inclusion criteria included Chinese singleton primiparas, age ranging from 20 to 35 years old, clean lochia, no obstetric complications, and no history of accepting PFMT during pregnancy and at postpartum 6–8 weeks period. Exclusion criteria included age less than 20 years old or more than 35 years old, non-Chinese nationality, multiple pregnancies, vaginitis and urinary tract infection, and mental incapacity. A total of 217 SUI primiparas at postpartum 6–8 weeks were interviewed (SUI was diagnosed by questionnaire). The PFM strength was measured by specially trained personnel using digital palpation (Modified Oxford scale:0–5 grade) and sEMG. According to participants’ willingness to PFMT and through some necessary coordination, the subjects were divided into 2 groups including the treatment group and the control group. In the treatment group, at-home PFMT was given every day under the guidance of specialized medical personnel and in hospital electrical stimulation plus biofeedback therapy was given twice a week for 5 weeks from 6–8 postpartum weeks to 11–13 postpartum weeks. The control group was not given pelvic floor exercise at home or in hospital. At postpartum 11–13 weeks, the PFM strength in the two groups was measured again using digital palpation and sEMG, and SUI was diagnosed by questionnaire again. All the investigation and examination results were recorded truthfully, including patient characteristics, history, and pregnancy delivery data.
The diagnosis of SUI
Diagnostic criteria [10]. SUI was diagnosed from the following four aspects. ① to test is urine routine was normal, ②to test whether there was nervous system disease, ③to test whether there were other diseases of urinary system, ④to diagnose whether the patient cannot help leaking urine during coughing, sneezing, laughing, changing position or upon sudden increase of abdominal pressure.
Determination of PFM strength using digital palpation
Digital palpation [11]. PFM was determined by specialized medical personnel using digital palpation. First of all, women were told to empty the bladder and took lithotomy position. Then the specialized personnel put the index and middle fingers 2–3 cm into the vagina and identify the levator ani muscle, separate the two fingers and fall on two sides of levator ani muscle, meanwhile, they put the other hand on the abdomen to make sure the abdominal muscle was relaxed. PFM contraction without any movement of the pelvis or visible contraction of the glutei, hip, or abdominal muscles was emphasized. According to contraction strength and retraction capability, the PFM strength was divided into 0–5 grades and 6 classes. The scale of pelvic floor muscle strength was described by Modified Oxford scale. (Table 1)..
Determination of pelvic floor muscle strength by sEMG
PFM sEMG was recorded using a small diameter vaginal probe with two metal sensors (Noraxon U.S. A. Inc.) with a preamplifier (band pass filter 20Hz–500Hz, Common Mode Rejection Ratio of >100 dB at 60 Hz, input impedance>100Mʊ, amplifier gain 500). a 16-bit analog to digital(A/D) converter with an 500Hz anti-aliasing filter was used. The probe was inserted using a small amount of antiallergic lubricant positioned laterally in the vagina. After cleansing the skin with an alcohol swab, round self-adhesive electrodes (silver chloride) were applied to the skin over the examined muscle. On the basis of guaranteeing the patients not make visible contractions of these muscles, the next two bipolar self-adhesive electrodes were located on the right side along muscle fibers of the rectus abdominis, hip adductor muscle and gluteus maximus.
Here below is the MVC procedure, and sEMG signal was recorded during each trial (Fig 1) [12]:
——a 10-second baseline sEMG recording.
——5 repeated short (quick flick) contraction with a 5-second pause between each contraction, average mean (MVC) (mean amplitude value of the active sEMG portions, which is calculated when the amplitude exceeds the threshold level predetermined as 50% between minimum and maximum amplitudes in each particular trial) is analyzed.
—–5 repetitions of 10-second voluntary contractions with 10 seconds of rest in between. Parameters measured: average mean (MVC).
—-a sustained 60-second contraction. The magnitude of external forces or loading is not sufficient to initially estimate forces generated by the pelvic floor muscle. The only way to ensure correct performance of the task is to use the maximal contraction and provide verbal encourage to maintain the contraction. Therefore, the instruction “pull up and in, and squeeze around the probe as strongly as you can until you hear the command now relax” is given during the trial. The average mean of contraction of the sEMG signal is analyzed (MVC).
—-a 10s relaxation (resting tone) immediately after the 60s contraction.
PFM training at home [4]
When SUI women in 6–8 weeks postpartum period was diagnosed, the specialists in our department of pelvic floor center would teach them how to contract their PFM by demonstrating vaginal palpation. At first, the women were told to empty the bladder and took lithotomy position, then the specialist placed her index finger into the vaginal and told the women to lift and squeeze around the finger. For Kegel exercise at home, a sustained 5-second contraction with 10-second pause was performed as a cycle, 10 cycles as a repetition, and 10 repetitions were the amount of training for one day with supine position or upright position. Such training was regularly carried out for 5 weeks at home. The PFMT at home was monitored by the specialists and nurses in our department through WeChat (the most popular online chat platform in China designed by Tencent Company).
Electrical stimulation and biofeedback [13,14]
PFM enforcement program in hospital was carried out by the help of biofeedback and electrical stimulation, and 10 implementations as a complete course. The PFM enforcement program was implemented 30 minutes every time, twice a week, and totally performed for 5 weeks. MyoTrac infiniti (SA9800) device (Thought Technology Inc., Montreal, Canada) was adopted in this experiment. The biostimulation feedback system is based on biofeedback technology, bioformatics principles and bioengineering technology. Safe and effective electrical stimulation combined with biofeedback technology was carried out through vaginal sensor, which could record PFM activity and pelvic floor muscle contraction strength and administer the strength of electrostimulation. The direct vaginal probe consisted of 3 reference electrodes on the iliac and two sides hypogastric skin guiding to prevent the abdominal or gluteus muscles contraction. A separate probe was used for each primiparas to prevent cross-infection. With the help of computer graphics, various parameters of the device were adjusted to make each woman feel the active and passive contractions of PFM and without feeling any pain or discomfort. The parameters of electrical stimulation included the pulse width of 20–40 us and low voltage of 40–80Hz. The electrostimulation included rapid contraction exercise of PFM (stimulation and interval time is 2 s:2 s) and continuous contraction exercise of PFM (stimulation and interval time is 5–8 s:10 s). The electrical stimulation therapy lasted for 20 min, followed by 10-min biostimulation feedback therapy. Each treatment of electrical stimulation plus biostimulation lasted 30 min, which was conducted two times per week, with a total of 10 times as a full course of treatment.
Testing procedure
The experiment consisted of two phases, including at-home PFM training which was carried out every day and in-hospital electrical stimulation combined with biofeedback therapy which was performed twice a week for consecutive 5 weeks
The statistical method
All the statistical analyses were carried out using the Statistical Package of Social Sciences software (SPSS Version 13.0 Inc., Chicago, IL, USA). The values and variables were reported as mean ± standard deviation. Student’s test was performed to compare the variables in Gaussian distribution. Chi-square test was used to evaluate the categorical variables. Wilcoxon test was used to evaluate the difference of the PFM function at postpartum 6–8 weeks and at postpartum 11–13 weeks. The difference was considered statistically significant at p<0.05. A two-sample test was performed to determine whether the mean in the treatment group was different from the mean in the control group. α = 0.05,𝛽 = 0.1,power = 0.90, sampling ratin = 1.