Developmental Potential of embryos does not Impact Pregnancy Outcomes, but it Affects Live Birth Rates in Frozen Blastocyst Transfer Cycles.

Objective: This study aimed to determine whether or not developmental potential impacts clinical outcomes, when good grade blastocysts from Days 5 and 6 were transferred in frozen embryo transfer (FET) cycles.

Methods: 654 women, including 460 (70.33%) on Day 5 and 194 (29.66%) on Day 6 were analyzed, in which 905 Day-5 and 274 Day-6 blastocysts were transferred. Only grade AA, AB, BA, BB quality and expansion grade between 3-6 (Gardner grading system) blastocysts survived and were included.

Results: The implantation rate was higher, 41.9% (379/905) in normal Day-5 compared to delayed Day-6 blastocyst transfers - 36.5% (100/274), but not significant (p=0.1). The clinical pregnancy rate was similar and not significant (p=0.4) in normal Day-5 (32.4%), compared to delayed Day-6 (35%). Miscarriage rates were higher in normal Day-5 (13.3%) compared to delayed Day-6 (6.3%) blastocyst transfers but were not significant (p=0.06). On the other hand, the biochemical pregnancy rate was significantly higher (p=0.001) in the delayed Day-6 blastocysts (16.7%) transfer group compared to patients with normal Day-5 (2.4%) blastocyst transfers. Two patients had ectopic pregnancies from the delayed Day-6 blastocyst transfer group. Live-Birth rates were significantly higher in Day-5 blastocysts compared to Day-6 (p=0.03).

Conclusions: The developmental potential of embryos should not be considered a negative influence on pregnancy outcomes, especially good grade blastocysts vitrified on Days 5 and 6. Fully expanded blastocysts on Day-5 are considered similar in terms of outcomes to delayed Day-6 blastocysts; however, live-birth rates are significantly higher in Day-5 blastocysts.