The Life Cycle of the Placenta


What Is a Placenta?

Dr. N. Natour, an OB-GYN from Baylor Medical Center in Irving, Texas, says the placenta is also referred to as the after-birth. “The placenta is an organ which provides the fetus with oxygen, water, and essential nutrients as well as providing a route for clearance of fetal waste products like carbon dioxide,” says Dr. Natour. “The placenta also produces multiple hormones and other factors essential to the maintenance of pregnancy.”

The placenta grows along the lining of the uterus and is attached to the baby by the umbilical cord. “The placenta is partially of fetal origin and partly of maternal origin,” says Dr. Natour. “The fetal portion is composed of highly specialized cells from the outermost embryonic membrane, which form projections that contain the fetal blood vessels. These projections are called chorionic villi. The maternal portion is formed by a modification of the lining of the uterus, and the fetal villi grow into the uterine lining.”

Basically, the placenta is made up of a combination of cells from the mother and the growing baby. Most doctors describe the placenta as the interface between the mother and the baby. “The placenta provides a metabolic interchange between the fetus and the mother without allowing direct mixing of maternal and fetal blood,” says Dr. Natour.

How Does Your Placenta Grow?

The placenta usually grows on the upper part of the uterus, though occasionally it grows on the lower part of the uterus and covers the cervix. This is called placenta previa. Ninety percent of the placenta previa diagnosed in the second trimester correct themselves by the end of the pregnancy. The baby’s umbilical cord forms on the side of the placenta nearest to the baby, attaching the baby to its life source.

Growing a healthy placenta takes the same care as growing a healthy baby—good nutrition and prenatal vitamins. The average placenta weighs about 1 pound by the end of the pregnancy. Smoking is detrimental to healthy placenta growth and should be avoided.

Placenta Problems

Most women will have no problems with their placentas during pregnancy. There are a few conditions, such as placenta previa, that mothers should be aware of.

Dr. Natour notes the following conditions:

  • The placenta can implant over the cervix, which is called a placenta previa. This may cause maternal hemorrhage necessitating a preterm delivery. All babies with a placenta previa are born by C-section. Your doctor can determine by ultrasound if you have a placenta previa.
  • The umbilical cord vessels can travel over the cervix within the placenta. This is called vasa previa and can cause fetal hemorrhage if these vessels break when the bag of water breaks. This condition is extremely rare.
  • Lastly, the placenta can start to separate from the uterus prematurely. This is called a placental abruption. This can cause maternal hemorrhage, and if the abruption is severe enough to prevent adequate oxygenation to the fetus, fetal damage can occur. Risk factors for placental abruption include smoking, cocaine use, and hypertension.