Placentas are a disposable organ that your body produces with the intention of discarding at the end of your pregnancy. Each new pregnancy brings a new placenta that will feed your baby in the 40 weeks to come. After 40 weeks, the function of the placenta can begin to diminish, and so your care provider may suggest you closely monitor the well being of both baby and placenta after that time.
One common misconception about placentas is that they shunt blood from the mother to the baby. This actually isn’t true—in a healthy placenta there is no sharing of blood. There are two sides of the placenta: the fetal and the maternal. Each are composed of tissues exclusively from one or the other. The maternal side of the placenta is embedded into the uterus and pulls nutrients from the mother’s blood supply the same way blood provides nutrients to all other organs. The mother’s blood coats the fetal blood vessels in blood, and then gas exchange takes place. No fluid is actually exchanged.
Starting at the meeting point of the fetal and maternal sides of the organ, the fetal side has tiny blood vessels that eventually feed into the two arteries and one vain that make up the umbilical cord. Once the baby and placenta are delivered and the cord is cut, your midwife will inspect the cord for these three vessels. She will also inspect your placenta to make sure that it is healthy and intact, and that no pieces of it have remained in the uterus.
Following the delivery of the placenta, your midwife will make sure that your uterus is contracting to be smaller and harder than it was when you still had a baby inside. It is important to keep in mind that your placenta left a wound inside of you and to follow directions for taking care of yourself after your birth!
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Yetter JF III. (1998). Examination of the placenta. American Family Physician, 57(5), 1045-1054.