“Freeze Only” — An Evolving Standard in Clinical In Vitro Fertilization

In recent years, the rates of pregnancy and live birth after the transfer of frozen embryos have improved,1 probably as a result of the use of vitrification for embryo cryopreservation.2 In addition, multiple reports have shown that adverse perinatal outcomes are less common in pregnancies after frozen-embryo transfer than after fresh-embryo transfer.3,4 Analyses of in vitro fertilization (IVF) data from the Centers for Disease Control and Prevention and the Society for Assisted Reproductive Technology suggest that the differences in outcomes between frozen and fresh cycles may be explained by the nonphysiologic, hormonally hyperstimulated, periconceptional milieu of fresh IVF cycles, . . .