Blastocyst Transfer

Background

IVF embryos are usually transferred on the second or third day following egg retrieval at the four- to eight-cell stage. The embryos must continue to grow for two or three more days to reach the blastocyst stage (50-150 cells) before they are ready for implantation into the uterine wall (endometrium).

Recent advances in IVF laboratory methods have allowed for the successful culture of embryos to the blastocyst stage. Blastocysts may have a better potential to implant into the uterine wall than earlier stage embryos. Many embryos stop growing at the four- to eight-cell stage, probably because of some inherent problem. Therefore, fewer embryos will have the ability to grow to the blastocyst stage. Those that successfully reach the blastocyst stage are probably more developmentally competent than earlier stage embryos. As well, their stage of development when replaced into the uterus is very similar to what it would be in a natural conception cycle.

What are the pros & cons of blastocyst transfer?
The advantage of attempting to grow embryos to the blastocyst stage is that they should have a greater chance of implantation because the stage of development matches the uterine environment. As a result, fewer embryos can be replaced which will minimize the risk of a multiple pregnancy

The disadvantage of attempting to grow embryos to the blastocyst stage is that fewer embryos will "survive" or grow to this stage (probably about 30 - 50% of the embryos). There is a possibility (up to 10%) that none will reach the blastocyst stage and therefore, no embryos will be available for transfer. The availability of "extra" embryos for freezing is also significantly reduced. There is an additional fee for blastocyst transfer.

Who is eligible for blastocyst transfer?
Couples who have had unsuccessful prior attempts with IVF or IVF/ICSI despite having many good quality eggs retrieved are being offered blastocyst culture as an alternative treatment. The ability to select the most viable embryos for transfer should improve their chance of achieving a pregnancy.

The embryos will be cultured in the IVF laboratory for 5 to 6 days after egg retrieval. At least 4 good quality embryos (6 to 8 cells) should be available on the third day after egg retrieval to maximize the chances of obtaining a blastocyst.

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