1. After fertilization the zygote divides by cleavage process to form blastomere. This condition is called Marula.
2. The morula enters the uterus and transforms to form a blastocyst. The outer layer of the blastocyst is called the trophoblast and the inner layer is called the blastocyst.
3. Within two days the blastocyst attaches to the endometrial epithelium of the uterus.
4. As the blastocyst attaches to the uterus, the trophoblast divides rapidly to form two layers. The inner layer is called cyto-trophoblast and the outer layer is called syncytio-trophoblast.
5. Syncytio-trophoblasts rapidly infiltrate the endometrial epithelium and endometrial stroma layers of the uterus.
6. Within seven days the endometrium of the uterus covers the blastocyst. As a result, the implantation is completed.
7. Trophoblasts divide rapidly to form numerous chorionic villi and amnion sheaths in the uterine endometrium.