I-7: Maximizing Pregnancy Rates with The Use of Vitrification and Comprehensive Chromosome Screening

Background: Vitrification and warming of blastocysts is an established procedure for the preservation of embryos during IVF. Vitrification is so successful that it allows for elective single embryo transfer (eSET) to be performed routinely, since the frozen embryos will be available with high implantation potential if the fresh embryo fails. Comprehensive chromosome screening (CCS) is also a procedure that can allow wider use of eSET, since patients can transfer a single euploid embryo to the uterus and expect high implantation rates. In the current study, we have combined CCS with vitrification of blastocysts at the time of biopsy, and examined outcomes for patients returning for a frozen embryo transfer with their chromosomally normal embryos. Materials and Methods: Blastocysts were biopsied and then vitrified on day 5 or 6 of development. Three to 7 trophectoderm cells were removed and sent for analysis to a genetics laboratory (Natera, Redwood City, CA, USA), and the embryos were vitrified using a Vitkit and Cryotips (both from Irvine Scientific, Santa Ana, CA, USA) shortly after biopsy. When patients returned for a transfer of the vitrified embryos, they were strongly encouraged to transfer one embryo regardless of their age. The embryos were warmed using a Warming kit (Irvine Scientific) and transferred within 1 hour of warming to the uterus on day 6 of progesterone in a natural or controlled cycle as appropriate. Results: From 95 warming cycles performed between Jan 2012 and March 2013, an overall clinical pregnancy rate of 67% and implantation rate of 57% was achieved, and most patients warmed and transferred 1 embryo. No differences were seen in the proportion of embryos that were abnormal on day 5 or 6, and the number of retrievals with biopsy decreased with patient age as expected, as did the number of euploid embryos. Conclusions: The combination of comprehensive chromosome screening and vitrification gave good pregnancy and implantation rates across all age groups. Older patients were less likely to have any embryos biopsied or to have normal embryos available after CCS, but they avoided unnecessary transfers. Overall, the combination of vitrification and CCS worked well and facilitated the widespread use of eSET, even in older patients.