Patient and cycle characteristics
From January 2016 to December 2019, 9832 frozen-thawed D3 embryo transfer cycles from a total of 23366 were analyzed, including 6013 short culture cycles (2-3 h of post-thawed culture) and 3819 long culture cycles (18-20 h of post-thawed culture) (Figure S1). The female age, duration of infertility and body-mass index were 20-45 years, 0-25 years and 12-42 kg/m² respectively. The detailed cycle characteristics of the different groups are shown in Table S1. Significant differences of average age between L and S groups were observed in the < 35, 35-39 and total age groups (P /CI = 0.001/0.112-0.416, 0.046/-0.218–0.002, 0.000/0.226-0.630 respectively), and the differences of body-mass index, natural cycle rate, primary infertility rate and duration of infertility were not significant in all age groups.