Blastocysts

Normally in IVF we transfer embryos on day 2 or 3 after egg collection when embryos are at the 2 to 8 cell stage of development. Once embryos are transferred we have no way of knowing what has become of them, many of them will stop growing once transferred and will not implant. They will be re-absorbed into the body without the patient even knowing.

In order to try and choose the embryos which have a better chance of success we are trying to extend culture in the laboratory until day 5 post egg collection. Embryos which are able to reach this stage are known as blastocysts. At this stage they will have many cells usually more than 100. We know from other groups who are growing embryos to the blastocyst stage that they have a better chance of implanting.

Until recently culturing embryos to the blastocyst stage of development has not been very successful, because for growth after day 3 embryos need media containing different nutrients. A suitable media has now been produced and other groups are reporting successful growth of embryos to the blastocyst stage and increased pregnancies.

Because the implantation rate of blastocysts is increased it may be preferable to only have 1 embryo transferred. However this may depend on the quality of the blastocysts for transfer.

Only about 50% of fertilized embryos will reach the blastocyst stage, so it may be that some patients will not have any embryos to transfer on day 5. In order to try and ensure you have an embryo transfer we will only culture embryos to day 5 if you have at least 10 fertilized eggs.

If you have blastocysts remaining after transfer on day 5 it will be possible to freeze them if they are of a suitable quality.