Clinical outcomes following frozen-thawed blastocyst transfers with blastocysts derived from different cell numbers on day 3: a retrospective cohort study

Purpose To evaluate clinical outcomes after frozen-thawed blastocyst transfer (TBT) with blastocysts which were derived from different cell numbers on day 3. Methods The study included 1444 patients undergoing single autologous frozen-thawed blastocyst transfer cycles, which were allocated to five groups according to the cell numbers on day 3 of the transferred blastocysts: ≤ 6-cell ( n = 109), 7-cell ( n = 169), 8-cell ( n = 811), 9-cell ( n = 136), and ≥ 10-cell ( n = 219). Results The LBR of the ≤ 6-cell group was found to be statistically lower than that of the 8-cell group in single TBT cycles which had been transferred with fair quality blastocysts (defined as 4BB according to Gardner’s grading scale) (41.28% vs 55.73%, P = 0.004), while the miscarriage rate was significantly higher for the ≤ 6-cell group compared with the 8-cell group (25.00% vs 13.74%, P = 0.02). No differences were found between the two groups in terms of cPR ( P = 0.06). However, for blastocysts categorized as high quality according to Gardner’s classification (defined as 4AA/4AB/4BA), cPR, LBR, and early miscarriage rates did not differ between the two groups ( P = 0.76, P = 0.44, P = 0.40, respectively). Conclusions When transferring blastocysts, an evaluation of the cleavage stage should be performed along with blastocyst morphology to shorten the time of conceiving.