Blastocyst culture

During the first days of in vitro development the embryo cells or blastomeres double in number every twenty hours or so. By the third day of culture the embryo will be made up of about eight cells of similar appearance.

The blastocyst is the embryonic stage reached between the fifth and sixth day of development after fertilisation of the oocyte by the sperm cell. At this point, the embryo is made up of more than 150 cells that differentiate into two distinct structures: the inner cell mass, which will develop into the foetus, and the trophoblast, which will give rise to the placenta.

Why is blastocyst culture performed?

During the early stages, embryos depend on the material provided by the maternal ovum for their growth. Those with the lowest chances of survival remain in the cleavage stage (cells) and do not continue their differentiation to the blastocyst stage.

Cultivating the embryos for 5 to 6 days allows for a ‘self-selection’ of the embryos with the highest probability of achieving pregnancy. Among those that reach the blastocyst stage, the embryologist selects the ones with the best morphology before transferring them to the mother's uterus.

These embryos are more developed and therefore have a higher implantation rate compared to embryos at day three. The tendency is to transfer a single blastocyst, thus reducing the possibility of twin pregnancy.