In vitro fertilization outcomes of frozen-thawed embryo transfer are better with hatched blastocysts than with hatching blastocysts

Abstract Purpose The aim of this study was to elucidate the effect of hatching status on in vitro fertilization outcomes in frozen–thawed blastocyst transfer cycles. Methods Frozen–thawed embryo transfer (FET) cycles performed at a single fertility center between 2016 and 2021 were retrospectively assessed. Analyses were restricted to 6821 frozen–thawed blastocyst transfers in women aged 24–47 years. For optimal comparability, double embryo transfer cycles consisting of one hatching and one hatched blastocyst were excluded. Implantation and pregnancy rates were evaluated and compared between subgroups, based on patients’ age (≤ 38 years vs. >38 years), blastocyst grade (good vs. bad grade) and number of transferred embryos (single embryo transfer [SET] vs. double embryo transfer [DET]). Results Hatched blastocyst transfer was associated with higher implantation and clinical pregnancy rates in the SET group (15.7% and 15.6%, respectively; p < 0.05). The transfer of two hatched blastocysts had a trend of higher implantation and clinical pregnancy rates, compared to the transfer of two hatching blastocysts (19.5% and 20.4%, respectively; p < 0.05) in the DET group. In the hatched blastocyst transfer group, the clinical pregnancy and implantation rates were higher, regardless of a woman’s age and embryo quality. Conclusion The IVF treatment outcomes improved when the blastocysts were hatched during FET cycles. Hence, hatched blastocyst transfer in FET cycles shall be considered as a superior method in IVF practice.