Blastocyst Freezing

A blastocyst is an embryo that has developed two different cell types, one type will become the placenta and the other will become the fetus. Embryos that develop to the blastocyst stage by day 5-6 may have a better chance of withstanding the freezing and thawing process. Blastocyst freezing is offered to IVF patients that have embryos remaining in culture after the transfer. The embryos that were not transferred originally may be frozen in the laboratory using a technique called cryopreservation. The embryos will be stored in the frozen state in liquid nitrogen until such time as deemed appropriate to transfer the thawed embryo(s) to the uterus. The replacement of these frozen, then thawed, embryos can result in a successful pregnancy.

In our laboratory we have an average survival rate of 60-70% for frozen-thawed zygotes and multi-cell embryos and over a 90% survival rate for blastocysts. Our ongoing/delivered pregnancy rate from frozen-thawed embryos is around 50%. The rate may be lower because we often use the best quality embryos during an IVF cycle and freeze the remaining embryos.