Blastocyst culture depends on quality of embryos on day 3, not quantity

A predictive model for high-quality blastocyst based on blastomere number, fragmentation, and symmetry

“…Although embryo evaluation criteria can help us select embryos [4], scholars have further claimed that the implantation rate and pregnancy rate for blastocysts are higher than those for embryos, indicating that blastocyst transfer is more advantageous than day-3 embryo transfer, particularly for high-quality blastocysts [5,6]. It has also been reported that a good day-3 embryo is apt to form a high-quality blastocyst [7,8]. However, not all good day-3 embryos can form high-quality blastocysts, partly because of the negative effect of being exposed to in vitro conditions for a long time [9].…”