An Overview of Placental Development

The placenta is an essential organ that develops in the uterus during pregnancy.  During the 9 months, it provides oxygens, nutrients and waste removal for the developing fetus.

This organ is usually attached to the top, back, side or front of the uterus while only in rare cases it is attached in the lower uterine region. Another important element is the umbilical cord which arises from the placenta and it connects the growing baby inside the womb to its mother.

The placenta begins to develop upon a process called implantation of the blastocyst (a structure that is formed during the first 5 days after fertilization) into the maternal endometrium.  Right after, the outer layer of blastocyst becomes the trophoblast which is the largest part of the placenta and provides nutrients to the embryo.

This layer is divided into 2 other layers:

• The underlying cytotrophoblast layer, which is the inner layer of the trophoblast and is formed by stem cells. The layer surrounding the blastocyst remains during the whole pregnancy, while ” daughter cells” proliferate to cover different roles;
• The overlying syncytiotrophoblast layer that is a multinucleated continuous cell layer that covers the surface of the placenta and is formed by the differentiation of stem cells of the cytotrophoblast layer. It functions as the barrier of the placenta and it develops during gestation.

All these processes take place in the first 2 weeks of pregnancy and continue to develop for the next 9 months. The placenta itself grows to adapt to the growing body of the baby.

The final stage, called the third stage of labor, is the expulsion of the placenta. It happens when the organ physiologically separates from the wall of the uterus during the labor and it all comes out from the birth canal 15-30 minutes after the baby is expelled.