Cryopreservation of day 2-3 embryos by vitrification yields better outcome than slow freezing.

Objective: To compare the outcome of vitrification versus slow freezing cryopreservation for cleavage stage day 2-3 embryos.

Methods: A retrospective observational study. Methods: All thawed embryos assisted reproduction cycles between January 2010 and December 2012 at a single IVF laboratory of a Tertiary Medical Center. Methods: Five hundred and thirty-nine cycles of day 2-3 thawed embryos. Methods: In 327 of the thawed cycles, the embryos were vitrified and in 212 of the cycles the embryos were derived from slow freezing embryos. Methods: Embryo survival rate, blastomere surviving rate and pregnancy rate.

Results: Embryo survival rate was significantly higher after vitrification compared with slow freezing (81.6%, 647/793 versus 70.0%, 393/562 embryos, p < 0.0001). The clinical pregnancy rate per ET was significantly higher following vitrification compared to slow freezing, 20.0%, 63/314 versus 11.9%, 23/193, respectively (p = 0.02).

Conclusions: Vitrification of day 2-3 cleavage stage embryos yields better cycle outcome in all the parameters compared to slow freezing.