0
blastocyst implantation
Blastocyst formation
When an embryo (fertilized egg) reaches the uterus, it is a hollow ball of about 100 cells called a blastocyst.
They make up the placenta that provides the blastocyst with nutrients.
A 5 day blastocyst will be 0.1 to 0.2 milleters (.003 to .005 inch) typically