COMPARISON OF THE CLINICAL OUTCOMES OF DAY 5 AND DAY 6 BLASTOCYSTS OF THE SAME GRADE IN THE FROZEN-THAWED CYCLES

Abstract

Background: The aim of this study was to discuss the clinical value of day 6 blastocysts by comparing the clinical outcomes of day 5 and day 6 blastocysts of the same grade in the frozen-thawed cycles. Methods：This was a retrospective study. Patients with day 5 or day 6 blastocysts were selected in the frozen-thawed cycles. Among them,1521 cycles were day 5 blastocyst transfer (D5 group), and 771cycles were sixth-day blastocysts transfer (D6 group). Patients in D5 and D6 group were both divided into 6 different groups according to the grade of blastocysts. Results：①In single blastocyst transfer cycles(SBT), the rate of clinical pregnancy and live birth of 4BC or 4CB in D5 group was higher than D6 group, with statistically significant difference (P<0.05). The rate of clinical pregnancy and live birth of 4BB in D5 group was comparable to D6 group(P>0.05). ②In double low-quality blastocysts transfer cycles, the rate of embryo implantation and multiple pregnancy of in D5 group was higher than D6 group, with statistically significant difference(P<0.05). The rate of live birth of 4BC+4CB in D5 group was higher than D6, with statistically significant difference(P<0.05). Conclusion: SBTs of day 6 of high-quality resulted in similar clinical and live birth rates compared to day 5. The clinical and live birth rates in SBTs of day 6 low-quality was lower than D5 with the same grade. The clinical outcomes of D5 low-grade double blastocysts were not better than D6 with the same grade, depending on the exact grade of the blastocysts.