Statistical analysis
Statistical analysis was performed using SPSS for Windows, version 25.0. A two-sided p-value of <0.05 indicated statistical significance. Continuous variables are presented as median (interquartile range) and categorical variables as number and percentage. Significance between groups was assessed by the McNemar test for categorical variables and the paired-samples t-test for continuous variables with a normal distribution. Wilcoxon rank sum test, a non-parametric test, was performed for continuous variables with non-normal distribution. Multivariable logistic regression, after adjust for confounders (presented in DAG), was performed to identify risk factors associated with sPTB. Kaplan–Meier curves were generated for GA at delivery according to the different subgroups (cervical dilation < 3cm and ≥ 3cm) and compared using the log-rank test to assess the prolongation of pregnancy observed in each subgroup.