Blastocyst transfer allows embryos to develop for longer outside the womb, reaching the ‘blastocyst’ stage before being implanted and increasing the chance of successful implantation. If you’ve produced good quality embryos in previous cycles but had issues with implanting in the womb, then blastocyst transfer could be right for you.
Like traditional IVF, a blastocyst starts with a fertilised egg. In this case, it will have been fertilised in a laboratory setting by an embryologist using either donor or partner sperm and has become an embryo.
In traditional IVF, an embryo might be implanted after two or three days of development.
However, a blastocyst is a more developed embryo – it has been developed in the laboratory for five or six days after insemination.
A day 5 or 6 embryo is a much more advanced structure than a 3 day old embryo, and a healthy blastocyst at this point may have the best chance of successful implantation.
What is a blastocyst transfer?
With a blastocyst transfer, the embryo has advanced to the 5 or 6 day stage. This means the embryo has divided many more times into many more cells over this period.
Blastocysts have a very thin outer shell thus potentially increasing the chances of blastocyst implantation into the uterine cavity. The real advantage is the potentially higher live birth rate associated with this type of transfer.
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, so they are considered to be a more "select" group of embryos with a higher chance of pregnancy.
In natural conception, an embryo is fertilised and formed in the fallopian tube, and generally reaches the uterus at around day 5, so a blastocyst may be more in line with the body’s natural timing.
What should an embryo do after transfer?
As the embryo develops into the blastocyst stage (late day 4 onward), it needs to escape the "shell" that once protected it. The blastocyst continues to fill with fluid and weakens the shell. Eventually the blastocyst hatches out of the shell (pictured) and is ready to implant into the lining of the uterus. This is thought to happen around 7-8 days post insemination.
Could it be right for me?
Blastocyst transfer is usually the best option for most people. And if you have experienced recurrent implantation failure, blastocyst extended culture gives us the opportunity to examine embryos over a longer period. If embryos arrest or become fragmented, this can help us identify any potential problems.
When a single embryo transfer is specifically required, typically for anyone who has a history of multiple pregnancy or a uterine issue, blastocyst transfer may be a particularly useful option.