Placenta: How it works, what's normal

The placenta plays a crucial role during pregnancy. Find out what it does, issues that might affect the placenta and how the placenta is delivered.

By Mayo Clinic Staff

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

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 area of the uterus. When this happens, it's called a low-lying placenta (placenta previa).

What affects placental health?

Various factors can affect the health of the placenta during pregnancy, with some under your control and some not. For example:

  • Maternal age. Some placental problems are more common in older women, especially after age 40.
  • A break in your water before labor. 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, also called your water breaking, 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 use. Certain placental problems are more common in women who smoke or use cocaine during pregnancy.
  • Abdominal trauma. Trauma to your abdomen — such as from a fall, auto accident 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 sometimes a concern. Here's what you need to know about these conditions:

  • Placental abruption. 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. 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 condition occurs when the blood vessels and other parts of the placenta grow too deeply into the uterine wall. This can cause severe blood loss during delivery.

    In aggressive cases, the placenta invades the muscles of the uterus or grows through the uterine wall. Your health care provider will likely recommend a C-section followed by removal of your uterus.

  • 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. Left untreated, a retained placenta can cause severe infection or life-threatening blood loss.

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:

  • 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 drugs.
  • Talk with your doctor about the potential risks 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. Also 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 continue uterine contractions and 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.

March 25, 2020 See more In-depth