Amniotic fluid is a liquid that surrounds and cushions the fetus (unborn baby) inside the uterus. It comes from the baby's kidneys, and it goes into the uterus from the baby's urine. The fluid is absorbed when the baby swallows it and through breathing motions.

The amount of fluid increases until the 36th week of pregnancy. After that, it slowly decreases. If the fetus makes too much urine or does not swallow enough, amniotic fluid builds up. This causes hydramnios.

Mild hydramnios may not cause any problems. Often, extra fluid that appears during the second trimester returns to normal on its own. Mild hydramnios is more common than severe hydramnios.

Hydramnios may occur in normal pregnancies with more than one baby (twins, triplets, or more).

Severe hydramnios may mean there is a problem with the fetus. If you have severe hydramnios, your health care provider will look for these problems:

• Birth defects of the brain and spinal column
• Blockages in the digestive system
• A genetic problem (a problem with the chromosomes that is inherited)

Many times, the cause of hydramnios is not found. In some cases, it is linked to pregnancy in women who have diabetes or when the fetus is very large.

Mild hydramnios often has no symptoms. Be sure to tell your provider if you have:

• A hard time breathing
• Belly pain
• Swelling or bloating of your belly

To check for hydramnios, your provider will measure your "fundal height" during your prenatal check-ups. Fundal height is the distance from your pubic bone to the top of your uterus. Your provider will also check your baby's growth by feeling your uterus through your belly.

Your provider will do an ultrasound if there is a chance that you may have hydramnios. This will measure the amount of amniotic fluid around your baby.

In some cases, the symptoms of hydramnios can be treated but the cause cannot be treated.

• Your provider may want you to stay in the hospital.
• Your provider may also prescribe medicine to prevent a preterm delivery.
• They might remove some of the extra amniotic fluid to relieve your symptoms.
• Nonstress tests can be done to make sure the fetus is not in danger (Nonstress tests involve listening to the baby's heart rate and monitoring contractions for 20 to 30 minutes.)

Your provider may also do tests to find out why you have extra fluid. These might include:

• Blood tests to check for diabetes or an infection
• Amniocentesis (a test that checks amniotic fluid)

Hydramnios may cause you to go into labor early.

It is easy for a fetus with a lot of fluid around it to flip and turn. This means there is a greater chance of being in a feet-down position (breech) when it is time to deliver. Breech babies can sometimes be moved into a head-down position, but they often have to be delivered by C-section.

You cannot prevent hydramnios. If you have symptoms, tell your provider so you can be checked and treated, if needed.

Amniotic fluid disorder; Polyhydramnios; Pregnancy complications - hydramnios

Buhimschi CS, Mesiano S, Muglia LJ. Pathogenesis of spontaneous preterm birth. In: Lockwood CJ, Copel JA, Dugoff L, et al, eds. Creasy and Resnik's Maternal-Fetal Medicine: Principles and Practice. 9th ed. Philadelphia, PA: Elsevier; 2023:chap 7.

Gilbert WM. Amniotic fluid disorders. In: Landon MB, Galan HL, Jauniaux ERM, et al, eds. Gabbe's Obstetrics: Normal and Problem Pregnancies. 8th ed. Philadelphia, PA: Elsevier; 2021:chap 28.

Updated by: LaQuita Martinez, MD, Department of Obstetrics and Gynecology, Emory Johns Creek Hospital, Alpharetta, GA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.