Placenta: The Basics

March 19, 2010

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Placenta: The Basics

by Elisa Ross, MD
reviewed by Marjorie Greenfield, M.D.

The placenta, commonly called the afterbirth, is the structure that attaches the baby to the inside of the uterus. Membranes attached to the baby's side of the placenta, also known as the amniotic sac, contain both the amniotic fluid and the baby. The blood vessels in the placenta join to form the umbilical cord, which enters the baby through the belly button ("umbilicus").

In the placenta, the blood of the mother and baby do not actually mix. Rather, the placenta--whose shape resembles a cauliflower--contains the baby's blood, while the cauliflowerlike surface is bathed in small lakes of the mother's blood along the inside wall of the mother's uterus. This closeness allows the circulating blood of the mother and that of the baby to exchange oxygen, nutrients, and waste products.

Ultrasound findings

Placental grade--The placenta can be seen by ultrasound. Sometimes it will appear to have tiny white flecks in it. These spots are called calcifications and are a normal sign of maturing. The more calcifications, the higher the grade assigned by the ultrasonographer. If calcifications are seen too early in the pregnancy, it can indicate that the placenta is aging too rapidly. In this case, the baby will be evaluated for growth at intervals to be sure he is getting the nutrients that he needs.

Location--Ultrasound also can show where the placenta is implanted within the uterus. It may be at the top (fundal), toward the back (posterior), or toward the front (anterior). All are normal.

If the placenta is near the front, the mother may not be able to feel her baby's kicks as early or as well as if it was implanted toward the back, because when the baby kicks, the force is muffled (as if he were kicking a pillow). This kicking is normal and does not harm the placenta.

If the placenta is so low in the uterus that it covers the cervix (placenta previa), it may cause vaginal bleeding and prevent delivery of the baby through the vagina.

Delivery
Usually the placenta is delivered shortly after the baby is born. Sometimes it can take more than half an hour, in which case the practitioner may reach inside to help it along. In rare instances, part of the placenta will stick to the wall of the uterus and will not spontaneously separate. In this case, a small operation may be necessary to scrape the placenta off the inside of the uterus (curettage). Even more rare is when the placenta grows into or through the wall of the uterus (placenta accreta or percreta), which also may require surgery.

Sometimes, despite a practitioner's best efforts to make sure that the entire placenta is out, a small piece gets left behind. It usually will be reabsorbed or eventually expelled. Signs of retained placental fragment include extra bleeding, tenderness of the uterus, or fever. Sometimes these signs don't occur until days or even weeks after childbirth. If you notice any of these problems, contact your practitioner.


RELATED INFORMATION

			Different Causes of Bleeding During Mid to Late Pregnancy
			Fetal Development
			Placenta, Cord and Amniotic Fluid

Created March 16, 2001
Reviewed April 01, 2003

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