Success rates and pregnancy outcomes in thawed embryos transferred after extended culture: cryopreserved embryos versus cleavage stage cryopreserved embryos

Success rates and pregnancy outcomes in thawed embryos transferred after extended culture: cryopreserved embryos versus cleavage stage cryopreserved embryos
There has been a general shift in assisted reproductive technology practice from cleavage stage embryo transfer to blastocyst stage transfer. The ability to culture embryos in vitro to the blastocyst stage has been aided by improvement in culture media and laboratory techniques. Blastocyst transfer is theorized to improve synchronicity of the endometrium and the embryo and facilitate self-selection of viable embryos (survival of the fittest), thus resulting in better live birth rates. This has also encouraged the use of single embryo transfer to decrease the risk of multiples and theoretically improve pregnancy outcomes (1).
Source: fertstert.org