A blastocyst results from an egg that has been fertilized, grown, and developed in the IVF Lab for 5 to 6 days. During IVF treatment, the process occurs in an Embryology Lab with the help of ICSI. Growing embryos to the blastocyst stage allows us to determine which embryos will be viable for continued development, allowing us to select the best embryo to transfer.
A blastocyst transfer occurs when the embryo is transferred to the uterus in an attempt at pregnancy through the IVF process.
One of the main benefits of blastocyst transfer seems to be an increased chance of implantation and thus achieving a pregnancy. This may very likely be a result of the effect that extended culture in the laboratory has on the embryos or the fact that the embryo is placed back into the uterus at a more physiologically appropriate stage.
Blastocyst transfer lowers the risk of multiples which are considered to be high risk pregnancies. Transferring a single embryo that has reached blastocyst stage has led to high pregnancy rates in good prognosis patients.
It is important to keep in mind that not all eggs that fertilize will end up growing for 5 days in the embryology laboratory, typically it is expected that between 30-50% of high quality day 3 (6-8 cell embryos) embryos develop to the blastocyst stage of growth in the embryology laboratory. Therefore, the decision to perform a day 3 or 5 embryo transfer is often simply based on the number of high quality embryos that a patient has growing in an IVF laboratory.