The Stages of Human Development: From Fertilization to Birth

Human development begins with fertilization, forming a zygote that undergoes cleavage to become a morula, then a blastocyst. The blastocyst implants in the uterus, marking pregnancy's start. It develops into germ layers, forming organs. The embryo becomes a fetus, growing rapidly until birth, which is triggered by oxytocin.

Explain the role of the placenta in fetal development.

What hormonal changes occur around nine months of development that initiate labor?