Statistical analyses
One sample of the Kolmogorov–Smirnov test was used to test the normal
distribution of continuous variables. Continuous variables were given as
mean ± SD if normally distributed, and as median (interquartile range)
if not normally distributed. Statistical comparison was carried out by
Student’s t-test, Mann–Whitney U-test for continuous variables and
chi-square test for categorical variables, where appropriate. And
logistic regression analysis was used to analyse factors predicting the
ongoing pregnancy rate. Statistical analysis was performed using the
Statistical Program for Social Sciences (SPSS Inc., Version 24.0,
Chicago, USA). The two-tailed value of P<0.05 was considered
statistically significant.