What is a blastocyst?
A Blastocyst is an embryo which has developed for 5-6 days in culture from the egg retrieval and has two distinct cell types, and a central fluid filled cavity.
Why are blastocysts important?
While the majority of fertilised eggs will develop into a three-day old embryo, only perhaps 40% of these embryos will develop into a blastocyst. Therefore, blastocysts are considered to be a more “select” group of embryos with a higher chance of pregnancy.
What is the advantage of blastocyst culture?
Sometimes it is not possible to select the best quality embryo(s) to transfer at the day 3 stage. This is because at this stage all the embryos can still look relatively similar and it is impossible to select which embryo is capable of forming a pregnancy over those which are unlikely to. In such circumstances there is a tremendous advantage to let the embryos develop on for another 48 hours and allow them to develop into blastocysts.
By letting the embryos develop to the blastocyst stage the embryologist will be able to make a better choice of which embryo(s) to transfer back. We achieve higher pregnancy success in doing this because those embryos that manage to become blastocyst in the lab have a higher potential to implant in the womb.
The 5 or 6 day blastocyst is a much more advanced structure than the 3 day old embryo and the real advantage of transferring blastocysts is the higher live birth rate associated with blastocyst transfer.