title: Improved outcome of frozen-thawed blastocyst transfer with Menezo's two-step thawing compared to the stepwise thawing protocol.
abstract: OBJECTIVE
  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%, P < 0.01). The percentage of gestational sacs resulting in live babies was higher with two-step thawing (76.6%) than with stepwise thawing (50%, P = 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.
authors.affiliation: Oak Brook Fertility Center, 2425 W. 22nd Street, Suite 102, Oak Brook, Illinois 60523, USA. jding@oakbrookfertility.com
authors.forename: Jianchi
authors.initials: J
authors.lastname: Ding
authors.forename: Michelle
authors.initials: M
authors.lastname: Pry
authors.forename: Nasir
authors.initials: N
authors.lastname: Rana
authors.forename: W Paul
authors.initials: WP
authors.lastname: Dmowski
mesh_terms: D000328:Adult; D001755:Blastocyst / Q000166:cytology / Q000502:physiology*; D015925:Cryopreservation / Q000379:methods*; D004624:Embryo Transfer; D005260:Female; D005307:Fertilization in Vitro / Q000379:methods*; D005615:Freezing; D006801:Humans; D011247:Pregnancy; D011256:Pregnancy Outcome; D012189:Retrospective Studies