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Placenta: How it works, what's normal

Medically reviewed on Apr 26, 2018

If you're pregnant, you might wonder what the placenta does and what factors can affect it. Get the facts about this important fetal organ.

What does the placenta do?

The placenta is an organ that develops in your uterus during pregnancy. This structure provides oxygen and nutrients to your growing baby and removes waste products from your baby's blood. The placenta attaches to the wall of your uterus, and your baby's umbilical cord arises from it. The organ is usually attached to the top, side, front or back of the uterus. In rare cases, the placenta might attach in the lower uterine region (placenta previa).

What affects placental health?

Various factors can affect the health of the placenta during pregnancy, some modifiable and some not. For example:

  • Maternal age. Certain placental problems are more common in older women, especially after age 40.
  • Premature rupture of the membranes. During pregnancy, your baby is surrounded and cushioned by a fluid-filled membrane called the amniotic sac. If the sac leaks or breaks before labor begins, the risk of certain placental problems increases.
  • High blood pressure. High blood pressure can affect your placenta.
  • Twin or other multiple pregnancy. If you're pregnant with more than one baby, you might be at increased risk of certain placental problems.
  • Blood-clotting disorders. Any condition that either impairs your blood's ability to clot or increases its likelihood of clotting increases the risk of certain placental problems.
  • Previous uterine surgery. If you've had a previous surgery on your uterus, such as a C-section or surgery to remove fibroids, you're at increased risk of certain placental problems.
  • Previous placental problems. If you've had a placental problem during a previous pregnancy, you might have a higher risk of experiencing it again.
  • Substance misuse. Certain placental problems are more common in women who smoke or use illegal drugs, such as cocaine, during pregnancy.
  • Abdominal trauma. Trauma to your abdomen — such as from a fall or other type of blow — increases the risk of the placenta prematurely separating from the uterus (placenta abruption).

What are the most common placental problems?

During pregnancy, possible placental problems include placental abruption, placenta previa and placenta accreta. These conditions can cause potentially heavy vaginal bleeding. After delivery, retained placenta is also sometimes a concern. Here's what you need to know about these conditions:

  • Placental abruption (abruptio placentae). If the placenta peels away from the inner wall of the uterus before delivery — either partially or completely — a condition known as placental abruption develops. This can deprive the baby of oxygen and nutrients and cause you to bleed heavily. Placenta abruption could result in an emergency situation requiring early delivery.
  • Placenta previa. This condition occurs when the placenta partially or totally covers the cervix — the outlet for the uterus. Placenta previa is more common early in pregnancy and might resolve as the uterus grows. Placenta previa can cause severe vaginal bleeding during pregnancy or delivery. The management of this condition depends on the amount of bleeding, whether the bleeding stops, how far along your pregnancy is, the position of the placenta, and your and your baby's health. If placenta previa persists late in the third trimester, your health care provider will recommend a C-section.
  • Placenta accreta. This condition occurs when the blood vessels and other parts of the placenta grow too deeply into the uterine wall. Typically, the placenta detaches from the uterine wall after childbirth. With placenta accreta, part or all of the placenta remains firmly attached to the uterus. This can cause severe blood loss after delivery. Your health care provider will recommend a C-section followed by removal of your uterus (hysterectomy). In aggressive cases, the placenta invades the muscles of the uterus (placenta increta) or grows through the uterine wall (placenta percreta).
  • Retained placenta. If the placenta isn't delivered within 30 minutes after childbirth, it's known as a retained placenta. A retained placenta might occur because the placenta becomes trapped behind a partially closed cervix or because the placenta is still attached to the uterine wall — either loosely (adherent placenta) or deeply (placenta accreta). Left untreated, a retained placenta can cause severe infection or life-threatening blood loss.
Placental abruption

The placenta is a structure that develops in the uterus during pregnancy. Placental abruption occurs when the placenta separates from the inner wall of the uterus before birth. Placental abruption can deprive the baby of oxygen and nutrients and cause heavy bleeding in the mother. In some cases, early delivery is needed.

Placenta previa

The placenta is a structure that develops in the uterus during pregnancy. In most pregnancies, the placenta is located at the top or side of the uterus. In placenta previa, the placenta is located low in the uterus. The placenta might partially or completely cover the cervix, as shown. Placenta previa can cause severe bleeding in the mother before or during delivery. A C-section might be needed.

What are signs or symptoms of placental problems?

Consult your health care provider during pregnancy if you have:

  • Vaginal bleeding
  • Abdominal pain
  • Back pain
  • Uterine contractions

What can I do to reduce my risk of placental problems?

Most placental problems can't be directly prevented. However, you can take steps to promote a healthy pregnancy. For example:

  • Visit your health care provider regularly throughout your pregnancy
  • Work with your health care provider to manage any health conditions, such as high blood pressure
  • Don't smoke or use illegal drugs
  • Talk with your doctor before deciding to pursue an elective C-section

If you've had a placental problem during a previous pregnancy and are planning another pregnancy, talk to your health care provider about ways to reduce the risk of experiencing the condition again. Tell your health care provider if you've had surgery on your uterus in the past. Expect your health care provider to monitor your condition closely throughout the pregnancy.

How is the placenta delivered?

If you deliver your baby vaginally, you'll also deliver the placenta vaginally — during what's known as the third stage of labor. After you give birth, you'll continue to have mild contractions. Your health care provider might give you a medication called oxytocin (Pitocin) to reduce postpartum bleeding. Your health care provider might also massage your lower abdomen to encourage your uterus to contract and expel the placenta. You might be asked to push one more time to deliver the placenta. If you have a C-section, your health care provider will remove the placenta from your uterus during the procedure.

Your health care provider will examine the placenta to make sure it's intact. Any remaining fragments must be removed from the uterus to prevent bleeding and infection. If you're interested, ask to see the placenta. In some cultures, families bury the placenta in a special place, such as their backyards.

If you have questions about the placenta or placental problems during pregnancy, talk to your health care provider. He or she can help you better understand the placenta's role during your pregnancy.

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