REPRODUCTIVE OUTCOMES FOLLOWING FROZEN-THAWED EMBRYO TRANSFER IS SUPERIOR WITH THE TRANSFER OF BLASTOCYSTS EXPANDED ON DAY 5 THAN ON DAY 6

Abstract

Abstract: To compare pregnancy and live birth rates between D5 and D6 transfer of frozen-thawed blastocysts in women undergoing ‘freeze-all’ cycles. This retrospective cohort study included 209 single autologous frozen–thawed blastocyst transfers. This cohort was divided into 2 groups based on the day of blastocyst expansion: (i) D5 blastocysts and (ii) D6 blastocysts. A ‘freeze-all’ strategy was adopted using GnRH antagonist cycles and vitrification as the method of freezing. Pregnancy rate was higher in D5 group as compared to D6 group, although not statistically significant (72.6% vs. 59.6%, respectively, p=0.078). Live birth rate was significantly higher in D5 group than in D6 group (66.9% vs. 48.1%, respectively, p=0.015). The rates of abortus, biochemical pregnancy and preterm birth were comparable between the groups. Live birth rate is superior when blastocysts expanded on D5 are used in frozen–thawed cycles, compared to those expanded on D6. The day of the blastocyst expansion appears to be an important predictor of pregnancy outcome and, thus, taken into account as well as D5 embryos should be given priority in frozen-thawed transfer cycles.