Extended culture of day 3 embryos improves live birth rate in in vitro fertilization-embryo transfer

To the Editor:Embryo development at the early cleavage stage is a complex and well-orchestrated biological process.During in vitro fertilization-embryo transfer(IVF-ET),embryos are routinely stratified according to morphological criteria and transferred on the morning of day 3 after fertilization.This stage of embryonic development is mainly regulated by maternal factors because the embryonic genome has not yet been fully activated.[1]Day 3 is a key period for embryos to accomplish embryonic genome activation(EGA).Embryos with higher developmental potential initiate EGA for subsequent development and implantation,while non-viable embryos undergo arrest.