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

Abstract

To compare pregnancy and live birth rates between D5 and D6 transfer of frozen-thawed blastocysts in women undergoing ‘freeze-all’ cycles. Our study, designed as a retrospective cohort study, evaluates single frozen thaw embryo transfer in 209 patients. The cohort group included in the study was divided into two according to the day of becoming blastocyst: (i) D5 blastocysts and (ii) D6 blastocysts. A ‘freeze-all’ strategy was adopted using GnRH antagonist cycles and vitrification as the method of freezing. The pregnancy rate was higher in the D5 group than the D6 group, although it was not statistically significant (72.6% vs. 59.6%, respectively, p=0.078). Live birth rate was significantly higher in the D5 group than in the 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 the priority in frozen thawed transfer cycles.

Keywords

• frozen embryo transfer
• live birth rate
• day 5 versus day 6
• blastocyst vitrification