Perinatal outcomes following transfer of human blastocysts vitrified at day 5, 6 and 7

Little information is available on perinatal outcome of cryopreserved day-7 blastocyst transfer. In the present report, perinatal outcomes for transfers of cryopreserved blastocysts by a vitrification method were examined with respect to the day of blastocyst expansion among on day 5, 6 or 7 before cryopreservation. We investigated 263 cycles of vitrified-warmed blastocyst stage embryo transfer performed between April 2005 and April 2009, which were reviewed retrospectively. There were 144 cycles with day-5 blastocyst, 100 cycles with day-6 blastocyst, and 19 cycles with day-7 blastocyst transfers. There were no differences among the vitrified day-5, day-6 and day-7 blastocyst transfer groups regarding mean number of embryos transferred, pregnancy rate, implantation rate and miscarriage rate. At this time, 71 deliveries have occurred with no reported abnormalities. There were 47 infants from 41 deliveries with day-5 blastocyst, 26 infants from 23 deliveries with day-6 blastocyst, and 8 infants from 7 deliveries with day-7 blastocyst. There were no differences among the three groups in the mean gestational age, preterm delivery rate and mean birth weight. These results indicated that blastocysts have similar inherent viability regardless of whether they develop by day 5, 6 or 7.