In vitro fertilization with single blastocyst-stage versus single cleavage-stage embryos

A randomized controlled trial is designed to determine whether there are differences in the rates of pregnancy and delivery between women randomly assigned to undergo transfer of a single cleavage-stage embryo and those assigned to undergo transfer of a single blastocyst-stage embryo. The results show that the transfer of a single blastocyst-stage embryo significantly increases the likelihood of pregnancy and delivery as compared with transfer of a single cleavage-stage embryo.