Vitrified-warmed blastocyst transfer cycles yield higher pregnancy and implantation rates compared with fresh blastocyst transfer cycles--time for a new embryo transfer strategy?

OBJECTIVE: To compare the clinical outcome of fresh versus vitrified-warmed blastocyst transfer (BT) cycles.
DESIGN: Retrospective study.
SETTING: Medical university affiliated hospital. PATIENT(S): Women aged less than 40 years undergoing BT cycles. INTERVENTION(S): Vitrification and warming of blastocyst with the Cryotop system. MAIN OUTCOME MEASURE(S): Clinical pregnancy rate (CPR), implantation rate (IR), and multiple pregnancy rate (MPR). RESULT(S): In 110 fresh BT cycles versus 136 vitrified-warmed BT cycles performed from January 2007 to March 2010, the IR and CPR of vitrified-warmed BT cycles were 37.0% and 55.1%, respectively, which were statistically significantly higher than the corresponding values of 25.2% and 36.4% obtained for fresh BT cycles. Additionally, the MPR was not statistically significantly different between vitrified-warmed and fresh BT cycles when a similar number of blastocysts was transferred to patients. CONCLUSION(S): Vitrified-warmed BT cycles resulted in statistically significantly higher CPR and IR compared with fresh BT cycles. A new embryo transfer strategy is therefore proposed whereby fresh BT would be avoided in the initial ovarian stimulation cycle. Instead, all the patient's available blastocysts would be vitrified-warmed and transferred in subsequent cycles.