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What is excess amniotic fluid (polyhydramnios)?

Amniotic fluid - the clear liquid in the sac surrounding a fetus - plays an important role in pregnancy. The fluid helps protect a developing baby and aids fetal muscle, limb, lung and digestive system development. The baby tumbles and moves in the amniotic fluid, and as the pregnancy progresses, the baby takes in and puts out amniotic fluid. The fetus swallows the fluid and "breathes" it into the lungs, then excretes fetal urine and "exhales" the fluid. After the 20th week of pregnancy, amniotic fluid is made up primarily of fetal urine.

In some cases, women may have higher than normal levels of amniotic fluid, which is called polyhydramnios. Polyhydramnios can be a sign of fetal malformations or genetic disorders, maternal diabetes, multiple gestation or other unknown causes.

Although most cases of polyhydramnios are mild and do not lead to poor pregnancy outcomes, women with more severe polyhydramnios can be at higher risk of complications including premature rupture of the membranes (when your water breaks before labor begins), placental abruption, preterm labor and delivery, growth restriction or stillbirth.

What causes excess amniotic fluid?

Polyhydramnios results from decreased fetal swallowing and/or increased fetal urine output, which leads to an excess of amniotic fluid. It has several causes, although doctors can trace the cause in only one third of cases.

Known causes can include the following conditions:

  • Fetal malformations and genetic disorders - Problems affecting the baby's swallowing and urine output may be due to gastrointestinal problems, neuromuscular disorders (such as anencephaly) or chromosome problem (such as Edwards syndrome or Trisomy 18) that causes heart, breathing and kidney problems, resulting from a birth defect or genetic disorder. These problems can affect how much fluid the baby takes in or how much fluid it puts out.
  • Maternal diabetes - Babies carried by mothers with diabetes may process extra glucose that crosses to the placenta if the mother's blood sugar is not controlled. The baby's pancreas makes more insulin, which allows the fetus to move more sugar into its bloodstream. As a result, the baby receives and stores more glucose than it would under normal circumstances and grows larger than average, which correlates with more urine output and higher amniotic fluid volume.
  • Multiples (twins or more) - Twins or multiples may not evenly share blood supply, so one baby can grow larger while the other(s) has restricted growth. The baby with restricted growth puts out less urine, and the other baby puts out more urine.
  • Fetal viral infections, fetal anemia, neuromuscular disorders or other problems

How common is excess amniotic fluid?

The condition occurs in one to two out of every 100 pregnancies. Doctors can diagnose it during a regular ultrasound and closely monitor women with excess amniotic fluid throughout pregnancy. Most cases are mild with only slightly higher levels of amniotic fluid than normal that slowly build up in the second half of pregnancy. Mild polyhydramnios resolves itself without treatment in 50% of cases.

More severe polyhydramnios is often caused by a fetal problem, which may be genetic, or by gestational diabetes. Women with a history of certain genetic defects or who have been diagnosed with gestational diabetes can be at higher risk of developing polyhydramnios.

What are the signs or symptoms of excess amniotic fluid?

Most women with polyhydramnios do not have tell-tale symptoms. Women with more severe cases may have stomach discomfort and breathing problems due to fluid buildup; the extra fluid causes the uterus to crowd the lungs and the organs in the belly. Your health care provider will most likely check amniotic fluid levels during regular prenatal checkups, rather than investigating symptoms on a one-off basis.

Excess amniotic fluid can be diagnosed in qualitative (based on a subjective visual evaluation) or quantitative (based on certain measurements) terms using an ultrasound exam. Amniotic fluid index (AFI) and single deepest pocket measurement techniques are two of the most common ways to quantitatively evaluate amniotic fluid levels. AFI is calculated by dividing the uterus into four quadrants and measuring the diameter of each vertical amniotic fluid pocket in centimeters.

Normal, oligohydramnios (low amniotic fluid) and polyhydramnios each have a specific measurement range. Doctors may measure in centimeters the horizontal distance from a right angle of the largest pocket of amniotic fluid using the single deepest pocket technique.

What are the treatment options for excess amniotic fluid?

Once a doctor diagnoses a woman with high amniotic fluid, he or she considers the severity, cause and gestational age of the baby. In about 50% of mild cases, polyhydramnios resolves itself during the pregnancy. Other times, doctors can resolve the condition by addressing the cause. For example, if a woman with diabetes has high blood sugar levels, lowering her blood sugar can reduce the amount of amniotic fluid the baby produces.

In some cases, health care providers will remove some amniotic fluid using amniocentesis (inserting a needle through the abdominal wall and using a syringe to remove some fluid) or will prescribe medication to lower fluid levels. Each approach carries certain risks. Amniocentesis carries a risk of infection and miscarriage. Medication can cause maternal side effects such as nausea and heartburn, and babies may suffer from ductus arteriosus constriction, in which a normal fetal structure that allows blood to bypass circulation to the lungs is obstructed.

If your health care provider thinks you have excess amniotic fluid, you will probably need extra monitoring during your pregnancy. Most women are monitored once a week, although some are monitored twice a week. Doctors may also use nonstress tests and/or biophysical profiles once every week or two to evaluate fetal well-being. The best thing you can do is attend all your prenatal care appointments. If you have diabetes, talk to your doctor about your increased risk of excess amniotic fluid.

What is the short- or long-term impact?

Most cases of excess amniotic fluid are mild and result in few, if any, complications. However, those with higher levels of fluid could experience one or more of the following effects:

  • Preterm rupture of the membranes (breaks or tears in the sac that holds the amniotic fluid; also called PROM)
  • Umbilical cord accidents (such as cord prolapse when the baby's umbilical cord is squeezed during delivery, limiting its blood and oxygen supply)
  • Preterm delivery
  • Placental abruption (the placenta peels away from the uterine wall before delivery)
  • Poor growth of the fetus
  • Higher chance of stillbirth
  • Cesarean delivery
  • Severe bleeding by the mother after delivery

Excess amniotic fluid may or may not indicate a problem with the baby or the pregnancy. If your physician does identify a problem, he or she may be able to address the complication before delivery.You and your health care provider can also work together to make plans for when the baby is delivered.

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Questions to Ask Your Doctor

  1. What causes high amniotic fluid during pregnancy?
  2. How is the level of amniotic fluid measured?
  3. How accurately can this condition be diagnosed?
  4. What are the signs or symptoms of high amniotic fluid?
  5. When am I most likely to get high amniotic fluid? Can the condition improve or change during the pregnancy? When?
  6. What are the risks to me or my baby as a result of this condition?
  7. What can I do to prevent or treat high amniotic fluid?
  8. What are possible complications or side effects of treatments for this condition?
  9. What should I expect before, during and after treatment?
  10. Are there activities or daily habits I should change due to this condition?

Our Medical Advisory Board

Wiser Pregnancy's physician advisors review all information on the site to ensure its accuracy, relevance, and consistency with medical best practices.

Michele R. Lauria, MD

Professor of obstetrics and gynecology and attending staff at the Dartmouth University Hitchcock Medical Center in New Hampshire

Linda Burke-Galloway, MD

Senior obstetrics and gynecology physician with the Florida Department of Health and medical malpractice consultant with the U.S. Department of Health and Human Services

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