Impact of embryo transfer time on clinical pregnancy outcomes in frozen embryo transfer cycles

Objective: This study aimed to investigate the correlation between transfer time (the duration from loading embryos into catheters to expulsion into the uterine cavity) during embryo transfer and the clinical pregnancy rate (CPR). Methods: Data were collected from 486 women who underwent 486 vitrified-warmed cycles, transferring two cleavage embryos cryopreserved with good morphological quality at a single center. The cohort was stratified into tertiles based on transfer time in seconds: T1 (15–27 seconds), T2 (28–33 seconds), and T3 (34–81 seconds). Associations between transfer time and pregnancy outcomes were evaluated using multivariable linear regression analysis. Results: Our findings revealed CPRs of 55.6%, 51.2%, and 41.1% across the tertiles, while implantation rates were 35.8%, 36.3%, and 25.5%, respectively. Transfer time was not independently associated with clinical pregnancy (odds ratio [OR] = 0.98, 95% confidence interval [CI] = 0.96–1.01). Following adjustment for potential confounders, the effect size (OR) remained 0.99 (95% CI = 0.97–1.01). Compared to the T1 (reference) group, the CPR in the T3 group was significantly lower ( P <0.05). Conclusions: Our study provides evidence on the impact of transfer time on pregnancy outcomes, with prolonged transfer times adversely affecting CPRs.