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Key Points

Polyhydramnios happens when there is too much amniotic fluid around your baby during pregnancy.

Having too much fluid can affect how your baby develops.

It can be caused by problems with the baby’s swallowing or heart rate, or preexisting diabetes. 

Your health care provider may notice this condition during an ultrasound.

In many cases, slight polyhydramnios goes away by itself.

Polyhydramnios is when you have too much amniotic fluid. Amniotic fluid is the fluid that surrounds your baby while they’re in your body before birth. It’s very important for your baby’s development.

How do you know if you have polyhydramnios?

Many women with polyhydramnios don’t have symptoms. If you have a lot of extra amniotic fluid you may have belly pain and trouble breathing. This is because the uterus presses on your organs and lungs. Other signs and symptoms include:

  • Feeling tightness in your stomach
  • Upset stomach or indigestion
  • Constipation (trouble moving bowels)
  • Peeing less frequently
  • Swelling in your leg, thigh, hip, ankle or foot
  • Having an enlarged vulva (the outer part of the vagina)

Your health care provider uses ultrasound to measure the amount of amniotic fluid. There are two ways to measure the fluid: amniotic fluid index (AFI) and maximum vertical pocket (MPV).

The AFI checks how deep the amniotic fluid is in four areas of your uterus. These amounts are then added up. If your AFI is more than 25 centimeters, you have polyhydramnios. The MPV measures the deepest area of your uterus to check the amniotic fluid level. If your MPV is more than 8 centimeters, you have polyhydramnios.

Ask your provider if you have questions about these measurements.

What problems can polyhydramnios cause?

Polyhydramnios may increase the risk of these problems during pregnancy:

  • Preterm birth – Birth before 37 weeks of pregnancy
  • Premature rupture of the membranes (PROM) – When the amniotic sac breaks after 37 weeks of pregnancy but before labor starts
  • Placental abruption – When the placenta partially or completely peels away from the wall of the uterus before birth
  • Stillbirth – When a baby dies in the womb after 20 weeks of pregnancy
  • Postpartum hemorrhage – Heavy bleeding after having a baby
  • Fetal malposition – When a baby is not in a head-down position and may need to be born via Cesarean section (also called Cesarean birth or C-section)
  • Severe breathing problems during pregnancy
  • Uterine atony – When the uterus becomes stretched out and can’t contract normally
  • Bleeding after delivery
  • Prolapsed umbilical cord – When the umbilical cord comes out of the vagina before the baby
  • Macrosomia – When the baby weighs more than 8 pounds, 13 ounces (4,000 grams) at birth
  • Shoulder dystocia – A birth injury that happens when one or both of a baby’s shoulders get stuck inside the pelvis during labor
  • Birth defects, including problems with the baby’s bones and genetic conditions

If you have polyhydramnios, your provider will monitor your condition closely during your pregnancy. They may perform a nonstress test. This test checks how your baby’s heart rate reacts when your baby moves.

What causes polyhydramnios?

In about half of cases, we don’t know what causes polyhydramnios. In other cases, we can identify a cause. Some known causes are:

  • Birth defects, including gastrointestinal and lung disorders, brain and nervous system problems and those that affect the baby’s swallowing. A baby’s swallowing keeps the fluid at a steady level in the uterus.
  • Preexisting diabetes – Having too much sugar in your blood
  • A mismatch between your blood and your baby’s blood, such as Rh disease and hemolytic disease of the newborn (sometimes called anti-Kell disease). Rh factor is a protein that’s found on some people’s red blood cells. If your red blood cells have the protein, you’re Rh-positive. If your red blood cells don’t have the protein, you’re Rh-negative. Being Rh-positive or Rh-negative doesn’t affect your health. But it can affect your baby during pregnancy if you’re Rh-negative and your baby is Rh-positive. Hemolytic disease of the newborn happens when red blood cells die too quickly.
  • Twin-to-twin transfusion syndrome (TTTS) – If you are pregnant with identical twins, this is when one twin gets too much blood flow and the other gets too little.
  • Problems with the baby’s heart rate
  • An infection in the baby
  • Problems with the placenta
  • Not enough red blood cells in the baby (anemia)

How is polyhydramnios treated?

When an ultrasound shows you have too much amniotic fluid, your provider does a more detailed ultrasound to check for birth defects and twin-to-twin transfusion syndrome.

Your provider also may recommend a blood test for diabetes and an amniocentesis. Amniocentesis is a test that takes some amniotic fluid from around the baby to check for problems, like birth defects and genetic conditions in your baby.

In many cases, slight polyhydramnios goes away by itself. Other times, it may go away when the problem causing it is fixed. For example, if your baby’s heart rate is causing the problem, sometimes your provider can give you medicine to fix it.

If you have polyhydramnios, you usually have ultrasounds weekly or more often to check amniotic fluid levels. You may also have tests to check your baby’s health.

Having too much amniotic fluid may make you uncomfortable. Your provider may give you medicine called indomethacin. This medicine helps lower the amount of urine that your baby makes, so it lowers the amount of amniotic fluid. Amniocentesis also can remove extra fluid.

If you have slight polyhydramnios near the end of your pregnancy but tests show that you and your baby are healthy, you usually don’t need any treatment. If your or your baby’s health is in danger, your provider may give you medicine to start your labor early.

Is polyhydramnios common?

About 2 out of 100 (2 percent) pregnant people have too much amniotic fluid. It usually happens when fluid builds up slowly in the second half of pregnancy. In a small number of women, fluid builds up quickly. This can happen as early as 16 weeks of pregnancy, and it usually causes very early birth.

Last reviewed: February, 2023