The blastocyst is an embryo that is at an advanced stage of development (5-7 days after fertilization). This embryo has started cellular differentiation, developing two different types of cells and a central cavity full of liquid (blastocele). The cells on the surface around the cavity are called trophoblast and will later become the placenta. The cells in the central zone are called the internal mass and the fetus develops from these cells.
The blastocyst culture and embryo transfer on the 5th day help select the embryos with the best quality and the best replacement potential, increasing significantly the possibility of pregnancy. High quality embryos that can reach the blastocyst stage are not more than 50% of the obtained embryos. This is why there is a risk of not obtaining an optimal embryo and making the transfer to the patient.
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