Recently, the development of more ideal culture media made it possible to perform embryo transfer at the blastocyst stage. This stage is the final developmental stage of the pre-implanted embryo prior to its implant in the endometrium and pregnancy.
When to apply it
This method regards couples ending up having lots of embryos available for transfer. In these cases, a few blastocysts (embryos), one or two, may be transferred to avoid multiple pregnancies without reducing the success rate.
The procedure at a glance
In particular, the blastocyst is the developmental stage the embryo reaches 5-6 days after the egg collection. At this stage, the embryo consists of 60-120 cells (early or complete blastocyst) separated into the outer cellular mass forming the placenta and the inner cellular mass forming the main embryo.
In standard IVF and microfertilisation, embryos are transferred to the endometrial cavity 2-3 days after the egg collection.
The advantage of embryo transfer at the blastocyst stage i.e. 5-6 days after the egg collection is that it allows us to select the highest-quality embryos (most healthy, morphologically intact and more developed embryos) since only genetically healthy and potentially capable to be implanted embryos will reach this stage (30-40%). Moreover, embryo transfer at the blastocyst stage mimics the natural reproductive process and provides better embryo-endometrium coordination.
The disadvantage is that it is likely that no embryos will survive at this stage –given that only a small amount of embryos (30-40%) reaches the blastocyst stage –and no embryo transfer will be performed.
This method has not yet resulted in better outcomes.