Improved Outcome of Frozen-Thawed Blastocyst Transfer with Menezo's two-step Thawing Compared to the Stepwise Thawing Protocol

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Abstract
Purpose : To compare the effects of two different blastocyst thawing protocols on implantation, pregnancy, and live birth rates. Methods : Ninety four consecutive frozen-thawed blastocyst transfers from 1996 to 2002 were retrospectively analyzed. Blastocysts were cryopreserved using Menezo's two-step slow-freezing protocol. Frozen blastocysts were thawed for transfer according to Menezo's stepwise or two-step protocol. Immediately after thawing, assisted hatching was performed and all embryos were cultured for 3 to 5 h before transfer. Only viable embryos were selected for transfer. Results : Implantation, pregnancy (determined by the presence of fetal cardiac activity), and live birth rates were significantly higher with two-step (25, 45.7, and 42.9%) than with stepwise thawing protocol (9.2, 18.6, and 16.9%, PP=0.04). Conclusions : We conclude that the two-step thawing protocol offers advantages over the stepwise method. The two-step thawing protocol dramatically increased embryo implantation potential, resulting in higher pregnancy rate, and subsequent live birth rate, after frozen blastocyst transfer.

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