A retrospective comparative study of double cleavage-stage embryo transfer versus single blastocyst in frozen-thawed cycles

This retrospective study aimed to compare the outcomes of day 3 double embryo transfer (DET) with single blastocyst transfer (SBT) during frozen embryo transfer (FET) cycles. A total of 999 women below the age of 38 years who underwent FET at Malaysia’s KL Fertility and Gynaecology Centre from January 2019 to December 2021 were analyzed. Patients with autologous eggs were recruited in the study. All the eggs were inseminated by intracytoplasmic sperm injection. The embryos were vitrified on day 3 cleavage-stage or blastocyst stage with Cryotop® method. The FET was performed following natural cycle (NC), modified natural cycle (m-NC), or hormone replacement therapy (HRT) cycles. The NC and m-NC groups received oral dydrogesterone for luteal phase support. There were no statistical differences in the rates of positive pregnancy, clinical pregnancy, and ongoing pregnancy between the two groups. However, implantation rates were significantly higher in the SBT group (50.1% versus 37.6%, p < 0.05). The day 3 DET group had significantly higher multiple pregnancy rates (28.7% versus 1.1%, p < 0.05). Subgroup analysis of embryo transfers performed following NC, m-NC, or HRT cycles showed similar results. This study suggests that SBT is the better choice for embryo transfers as it had higher implantation rates and its pregnancy rates were similar to day 3 DET. The SBT also significantly reduced the incidence of multiple pregnancies without compromising pregnancy rates.