High Amniotic Fluid During Your Third Trimester

High Amniotic Fluid

Excessive volume of amniotic fluid occurs in about 0.2-3.5% of expecting moms. Amniotic fluid surrounds your baby in the womb. It helps your baby’s lungs develop, encourages bone and muscle growth, and maintains a constant temperature for your baby. The volume of amniotic fluid will continue to increase throughout pregnancy, reaching a maximum at 34 to 36 weeks. However, some expecting moms can have too much amniotic fluid, called polyhydramnios. Expecting moms with polyhydramnios often do not have symptoms, but severe cases may cause stomach pain or difficulty breathing because the uterus is applying pressure to the organs and lungs.

How do I know if I have polyhydramnios?

Your healthcare provider will use an ultrasound to determine if you have polyhydramnios by measuring the amount of amniotic fluid using either the amniotic fluid index (AFI) or the maximum vertical pocket (MPV). You are considered to have polyhydramnios if your AFI is greater than 24 centimeters or your MPV is more than 8 centimeters.

What are the risks to my baby?

Polyhydramnios during the third trimester of pregnancy can cause many health problems in your baby or complications with your delivery. Even mild polyhydramnios that occurs at or beyond 34 weeks of pregnancy has been associated with problems.

The following are problems that can occur due to polyhydramnios:

  • Abnormalities in your baby’s heart rate
  • Problems with your baby’s breathing
  • Stillbirth (when a baby dies in the womb after 20 weeks of pregnancy)
  • Premature birth (when your baby is born before 37 weeks of pregnancy)
  • Prolonged first stage of delivery
  • The need for delivery by C-section
  • Shoulder dystocia (a complication with delivery where your baby’s head is delivered vaginally, but his or her shoulders get stuck inside your body)
  • Placental abruption (a serious condition where the placenta separates from the wall of the uterus prior to delivery)
  • Premature rupture of membranes (when the sac holding your baby and the amniotic fluid breaks open after 37 weeks of pregnancy but prior to the start of labor)
  • Severe bleeding in the mom after birth

What causes polyhydramnios?

About 50-60% of cases of polyhydramnios occur spontaneously and the cause is unknown. The remaining cases of polyhydramnios are caused by different diseases that may be present in either the mom or the baby. An underlying disease is detected in 91% of expecting moms with moderate to severe polyhydramnios, compared to only 17% of expecting moms with mild polyhydramnios. Some of the underlying diseases lead to polyhydramnios because your baby is either unable to swallow properly or your baby has increased urine production, resulting in a higher than normal volume of amniotic fluid. Under normal conditions, the volume of amniotic fluid is maintained due to a balance between its production and absorption. Fluid is produced by your baby’s urine and liquid from your baby’s lungs. Your baby then swallows some of the amniotic fluid to return the volume back to normal. In addition to diseases that interfere with your baby’s ability to swallow or increase your baby’s urine production, other underlying diseases or conditions can also lead to polyhydramnios.

The following are potential causes of polyhydramnios:

  • Expecting moms who have diabetes
  • Viral infections in the baby, such as cytomegalovirus, parvovirus B19, or rubella
  • Other infections in the baby, including toxoplasmosis or syphilis
  • Genetic disorders in the baby
  • Fetal macrosomia (when a baby weighs more than 8 pounds, 13 ounces at birth)
  • Birth defects in the baby’s digestive system or nervous system (brain), which interferes with his or her ability to swallow
  • Babies who have anemia (anemia results in higher urine production)
  • Twin-to-twin transfusion syndrome (a condition that causes one twin to get too much blood flow and the other twin to not get enough)
  • Rh sensitization

How is polyhydramnios treated?

Expecting moms who are diagnosed with polyhydramnios will be monitored carefully. A nonstress test can check how your baby’s heart rate reacts when your baby moves. Other tests may monitor the volume of amniotic fluid along with your baby’s movement and breathing patterns. Mild cases of polyhydramnios usually do not require treatment and your delivery will be normal. If there is a specific condition causing your polyhydramnios, such as diabetes or an infection, your doctor will likely treat those conditions to help manage your symptoms.

If you have more severe polyhydramnios, you may experience shortness of breath, stomach pain, or preterm labor. These cases may require treatment to relieve symptoms and reduce the likelihood of preterm birth. An amniocentesis, where a needle is used to directly remove excess amniotic fluid, may be performed in some cases. However, this could cause preterm labor, premature rupture of membranes, placental abruption, or sepsis (a blood infection). Removing extra amniotic fluid is also only a temporary solution and the excess fluid will often return.

A nonsteroidal anti-inflammatory medication (NSAID), called indomethacin, can sometimes be used to treat polyhydramnios by decreasing the amount of urine and lung fluid produced by your baby. Currently, this medication is not frequently used due to side effects that this medication can cause in your baby, including problems with kidney and heart function. If this medication is used, your baby’s heart may need to be monitored. Indomethacin is not recommended past 31 weeks of pregnancy because it can cause health problems in your baby.


If you are diagnosed with polyhydramnios, your doctor will continually monitor both you and your baby to avoid complications with your delivery or health problems in your baby. You may need to have ultrasounds at least once per week to check your amniotic fluid levels. Additional tests may also be provided to check the health of your baby.

Brittani Zurek
Dr. Brittani Zurek earned her Doctor of Pharmacy from the University at Buffalo School of Pharmacy and Pharmaceutical Sciences. She currently works as a medical writer, specializing in disease management and medication therapy. Brittani also writes continuing education modules for healthcare professionals. She enjoys hiking and spending time outdoors in her free time.

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