Intravaginal Electrical Nerve Stimulation to Achieve a Voluntary Contraction in Women With Non-contracting Pelvic Floor: a Randomized Controlled Trial

This is a randomized controlled trial. A simple randomization procedure will be conducted using computer generated list. This list will be kept with a secretary not involved with the research. A concealed allocation will be performed. All participants will be recruited at Rehabilitation Center of the Clinical Hospital of Ribeirão Preto Medical School, University of São Paulo. The primary outcome of the study will be vaginal palpation, to differentiate women capable or not capable to perform a PFM contraction. The secondary outcome will be measured using the ICIQ- UI SF questionnaire.

To analyze the proportions of improvement after the intervention in relation to primary outcome we will consider the proportion of women with values equal or above 2 and 3 as specified in the outcome measure section, using the modified oxford grading scale. The sample size calculation will be done based in a pilot study after the study initiate (after registration) considering we found no data from a RCT investigating exactly the same intervention. The study of Vasconcelos et al. (2017) that investigated a similar intervention in the same population performed a sample size calculation using a test of differences between proportions and Fisher's exact test based in the proportion of change in the group receiving electrical stimulation ( 0.35 point) and in the control group (CG) (0.13 point). Considering a significance level of 5% and 80% test power, in the comparison between the intervention group (IG) and control group (CG), the minimum number indicated was 61 participants per group; however as the intervention was not exactly the same and the control group received instructions to perform home training we intend to do this calculation again based in a pilot sample after the study initiate (after registration).

As stated before in the initial registration, the sample size calculation was conducted based on a pilot test carried out by the researcher. The sample calculation was used for qualitative data (primary outcome measure) and non-paired sample based on the proportion of improvement after the intervention. The sample calculation compared n=14 in the control group and n= 9 in the intervention group. Considering the proportion of improvement, after intervention, in women with values equal or above 2 is suggested that a sample size of 14 participants per group would be adequate to see between group differences at power=0.90 and α=0.05. In a second situation, the proportion of improvement will be considered as a value equal or above 3, in this case a sample size of 28 participants per group would be adequate to see between group differences at power=0.80 and α=0.05, and 37 participants per group would be adequate to see between group differences at power=0.90 and α=0.05.

Data analysis The data will be analyzed initially through descriptive statistics, which will enable the characterization of the sample regarding the variables collected. This methodology has as basic objective to synthesize a series of values of the same nature, allowing a global view of the variation of these values, organizing and describing the data through tables of frequencies and descriptive measures.

To verify the association between the categorical variables, the data will be submitted to Fisher's exact test. The association quantification will be measured through logistic regression models, where the crude odds ratio with its respective 95% confidence intervals will be calculated.