Statistical analysis
There’s no previous study using lactobacilli supplementation during frozen-thaw ET cycles. Therefore, we hypothesized that the pregnancy rate in the intervention group would increase to 50% from the baseline (control group) rate of 34.2% in our clinic. To detect this difference with a significance level of 0.05 and a power of 0.8, a sample size of 153 patients per group is needed. Considering a 10% loss to follow-up for each additional cycle, 170 patients were included in each group. Statistical analyses were performed by using IBM SPSS Statistics for Windows (version 21.0; IBM Corp., Armonk, N.Y., USA). All tests of significance were two-tailed with a 