What does it mean that an embryo has reached blastocyst stage?

The blastocyst is the early stage of embryo development, which occurs on day 5 of development.

This stage is crucial for the implantation of the embryo in the uterus and its subsequent growth and development. 

Improvement in the in vitro culture media and lengthening of culture time to blastocyst has increased success rates in pregnancy, as blastocyst transfers are more likely to implant.

Embryologists will evaluate the blastocyst according to the morphology of its cells and its degree of expansion. The high quality blastocysts can achieve a pregnancy rate greater than 60% with the transfer of a single embryo.