The blastocyst stage is characterized by the presence of a blastocyst cavity, outer cell mass and inner cell mass. Embryonic stem cells are derived from the inner cell mass of the blastocyst.

In the experiments, foetuses were surgically delivered and their sex was found to have been correctly predicted at the blastocyst stage. You have full access to this article via your institution.

The study, now published in Evolution, Medicine, and Public Health, indicates that between 200 and 5,000 sperm can reach the ...