Yes. It is part of the development of the embryo.
in the uterus. In endometrium.
amniotic thickening
No. The uterus is the only organ capable of supporting the implantation of the blastocyst, which gives it the oxygen and nutrients it needs to develop into an embryo.
C
Blastocyst.
Cells up to 8 cell stage in human embryo can develop in any kind of cell in body. Inner cell mass in blastocyst can develop into any kind of cell in human body.
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
Blastocyst. Each of those cells will eventually become a different part of the baby's body as they each multiply, creating muscle, bone, and organ tissues.
I'm sure it may be possible to have twins at the time of feritilzation, but it is highly unlikely that two fetuses would survive in the same egg.