Although the amount of data for this subject is limited, the results are sufficient to show a trend toward support of the conclusion, re-freezing blastocycts from frozen thawed zygotes is highly warranted.  I would suggest an expansion in several areas; specifically, thawing methods, culture methods and conditions, and culture media used throughout the study.  Further expansion of the data based on the numbers of embryos originally frozen at the zygote stage, ie, were preganancy rates higher for patients with more embryos frozen at the PN stage?  Were there differences in embryo quality that could be discussed, what was the grading criteria?  What was the percent of embryos that developed to blastocysts of transferrable quality from the zygote stage?  What was the regime of uterine lining support for the frozen embryo transfer cycles? 

MSc in Clinical Embryology, embryologist for 25 years, extensive research in the area of oocyte and embryo cryopreservation and vitrification, embryo culture and pre-implantation genetic diagnosis.  Certified Embryology Laboratory Director/Technical Supervisor for Embryology and Andrology laboratories thought American Board of Boianalysts.