The impact of post-thaw culture time on clinical outcomes of embryos at different developmental stages

Purpose This study aims to investigate the effect of post-thaw embryo culture time on the clinical outcomes of embryos at different developmental stages. Methods This study adopted a retrospective analysis design, in which frozen embryo transfer cycles were divided into four subgroups: single cleavage-stage embryo transfer cycles, double cleavage-stage embryo transfer cycles, single blastocyst transfer cycles, and double blastocyst transfer cycles. Univariate and multivariate analyses were performed to evaluate the effect of post-thaw culture time on live birth rate, gestational age at birth, birth weight, and body length at birth within each subgroup. The live birth rate was defined as the primary outcome. Results In double cleavage-stage embryo transfer cycles (n=936), the <4h post-thaw embryo culture group had a significantly lower live birth rate (45.1%) than the ≥4h group (57.2%), with P = 0.001. After adjusting for confounding factors in the multivariable regression model, post-thaw culture time remained significantly associated with live birth rate ( P = 0.008), and the adjusted OR (95% CI) was 1.524 (1.117–2.081). In single blastocyst transfer cycles (n=688), the <4h post-thaw embryo culture group had a significantly higher live birth rate (47.2%) compared with the ≥4h group (34.3%), with P = 0.017. After adjusting for confounding factors, post-thaw culture time still maintained a significant association with live birth rate ( P = 0.003), and the adjusted OR (95% CI) was 0.493 (0.308–0.788). A statistically significant interaction was detected (adjusted interaction OR = 0.424, 95%CI 0.272–0.663, P<0.001), confirming that the effect of post-thaw culture time on live birth rate differs between cleavage-stage and blastocyst-stage embryos. Conclusion Post-thaw culture time significantly impacts live birth rates in both double cleavage-stage embryo transfer cycles and single blastocyst transfer cycles, and the effect varies according to the embryonic developmental stage.