Impact of Embryo Blastomere Number and D2 or D3 Cryopreservation after in Vitro Fertilization on the Clinical Outcomes of the Frozen-thawed Embryo Transfer

Objective: To explore the impact of embryo blastomere number at cryopreservation, and different cryopreservation time on day 2(D2) or day 3(D3) after in vitro fertilization,on the clinical outcomes of the frozen-thawed embryo transfer(FET). Methods:This is a retrospective analysis on 417 FET cycles. The patients were respectively divided into different groups according to cryopreservation time after in vitro fertilization,embryo blastomere number and good-quality embryo number. The clinical outcomes of the embryotransfer were compared. Results:The embryo survival rate and total blastomere survival rate in the group of the blastomere number exceeded 4-cells on D2 after frozen-thawed were significantly higher than those in the group of the blastomere number less than 4-cells(89.35% vs. 79.11%,42.01% vs. 30.22% respectively,P0.05).Compared with the group of blastomere less than 6-cells on D3,the group of blastomere exceeded 6-cells on D3 had higher embryo survival rate and total blastomere survival rate(86.52% vs. 72.43%,41.13% vs. 31.07%,P0.01). The good-quality embryo rate on D2(56.84%) was significantly higher than that on D3(48.82%),while the clinical pregnancy rate on D3(38.52%) was significantly higher than that of D2(27.61%). There was no significant difference in the embryo survival rate and abortion rate between D2 and D3(83.50% vs. 79.44%,10.81% vs. 10.09%,P 0.05) after frozen-thawed embryo-transfer. More good-quality embryos were transferred,higher the clinical pregnancy rate and multiple pregnancy rate obtained(P0.05). Conclusions:Cryopreservation of more than 4 blastomeres on D2 and more than 6 blastomeres on D3 could get better frozenthawed effect. The clinical outcomes of D3 cryopreservation embryo after FET were superior to D2 embryo.