Data processing and analysis
All collected data were rechecked for completeness and coded. Then the data were entered and cleaned using Epidata 3.1 software. Data are expressed as mean ± standard deviation, or median (25th-75th percentile). The normality of variables was assessed. Differences between two groups were compared with the Student’s t-test and the Mann–Whitney U test for continuous variables: mean and median, respectively, and with the χ2 test or Fisher’s exact test for categorical variables. We used the Spearman coefficient to assess the correlation between UR rate and VBAC rate. Multiple logistic regression analysis was performed to examine the influence of the symptoms as variables on UR. Odds ratios (OR) and Mean differences (MD) are presented with 95% confidence intervals (CI) Statistical analyses were performed using SPSS software, version 22.0 (SPSS Inc., Chicago, IL, USA). A p value of less than 0.05 was considered statistically significant.