Embryo vitrification and thawing
For Day 3 embryos, our laboratory procedure of vitrification and warming
was the same as the method used for human oocytes as reported by Tong et
al. previously (32). For blastocysts, a glass micro-needle was used to
collapse the blastocyst before vitrification. The following steps were
the same as for the Day 3 embryos.
Embryo quality was graded as 1(good), 2(reasonable), or 3(moderate)
according to the number of cells, degree of fragmentation and renewed
development of the embryo. This standard was based on the ESHRE Istanbul
consensus on embryo assessment (33).