Post-thaw culture has no beneficial effect on frozen embryos transfer outcomes comparing to same embryonal age non-cultured frozen-thawed embryos

Purpose: To assess the impact of post-thawing embryo culture on frozen embryo transfer (FET) outcomes. Methods: A retrospective cohort study including 678 consecutive FET cycles performed between the years 2004 and 2017 was conducted. Patients older than 45 years old were excluded. FET cycles were stratified as follows: (1) two-day (2d) embryos thawed and cultured to three-day (3d) versus 3d embryos thawed and transferred; (2) 2d or 3d embryos thawed and cultured to blastocysts versus blastocysts thawed and transferred. A p-value <.05 was considered statistically significant. Results: Maternal age, BMI, smoking, and basal FSH of the 2d and 3d cultured embryo group (n = 110) and the 3d non-cultured embryo group (n = 189) were comparable. Endometrium preparation protocols and the achieved endometrial thickness did not differ between groups. Pregnancy rate, implantation rate, clinical pregnancy, live birth rate, abortions, multiple pregnancies, perinatal outcomes, and birth weight were comparable. The 2d and 3d embryos cultured to blastocyst (n = 41) compared to non-cultured blastocyst (n = 338) showed that the non-cultured blastocyst patients had higher smoking rates and longer follicular phase. Endometrial thickness was comparable. The 2d and 3d embryos cultured to blastocyst stage had higher multiple pregnancies rate compared to the blastocyst non-cultured group, whereas pregnancy rate, implantation rate, live birth rate, miscarriages, perinatal outcomes, and birth weight were comparable. Conclusion: We could not demonstrate that the post-thaw culture had a significant impact on the outcome of FET cycles.