Blastocyst development rate influences implantation and live birth rates of similarly graded euploid blastocysts.

Objective: To determine whether the blastocyst development rate, as assessed by the day of trophectoderm biopsy (day 5 vs. day 6), affects the live birth rate (LBR) of similarly graded euploid blastocysts.

Design: Retrospective cohort study.

Setting: Academic medical center.

Patient(s): Patients who underwent frozen-thawed single euploid blastocyst transfers from 2013 to 2016 were included. Blastocyst morphologic grading was performed on day 5 or day 6 before the biopsy, with embryos designated into the following groups: good (3-6AA, 3-6AB, and 3-6BA), average (2-6BB), and poor (2-6BC and 2-6CB).

Intervention(s): Frozen-thawed embryo transfer.

Main Outcome Measure(s): Implantation rate (IR) and LBR.

Result(s): A total of 701 frozen-thawed single euploid blastocyst transfer cycles were included. Cycles in which day 5 blastocysts were transferred (n = 366) were associated with a significantly higher LBR than those in which day 6 blastocysts were transferred (n = 335; 60.4% vs. 44.8%). The odds ratio remained significant after controlling for all confounders, including the blastocyst grading. Furthermore, there was a significant difference in LBRs between good-quality, average-quality, and poor-quality blastocysts (67.8%, 53.4%, and 29.5%, respectively). Embryos reaching good-quality blastocysts on day 5 yielded significantly higher LBR (72.8% vs. 56.5%) and IR (77.7% vs. 58.7%) compared with those reaching similar quality blastocysts on day 6. Similarly, day 5 average-quality embryos conveyed a significantly higher IR compared with day 6 embryos of the same quality (64.4% vs. 53.4%).

Conclusion(s): In addition to aneuploidy assessment, the speed of embryo development to the blastocyst stage and an evaluation of blastocyst morphology are critical to selecting the best embryo.