Merck Manual

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Antonette T. Dulay

, MD, Main Line Health System

Last full review/revision Oct 2020| Content last modified Oct 2020
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Polyhydramnios is excessive amniotic fluid; it is associated with maternal and fetal complications. Diagnosis is by ultrasonographic measurement of amniotic fluid. Maternal disorders contributing to polyhydramnios are treated. If symptoms are severe or if painful preterm contractions occur, treatment may also include manual reduction of amniotic fluid volume.

Causes of polyhydramnios include the following:


With polyhydramnios, risk of the following complications is increased:

Risks tend to be proportional to the degree of fluid accumulation and vary with the cause. Other problems (eg, low Apgar score, fetal distress, nuchal cord, malpresentation requiring cesarean delivery) may occur.

Symptoms and Signs

Polyhydramnios is often asymptomatic. However, some women, especially when polyhydramnios is severe, have difficulty breathing, and/or painful preterm contractions. Sometimes the uterus is larger than expected for dates.


  • Ultrasonographic measurement of amniotic fluid index (AFI)

  • Comprehensive ultrasonographic examination, including evaluation for fetal malformations

  • Maternal testing for causes suspected based on history

Polyhydramnios is usually suspected based on ultrasonographic findings or uterine size that is larger than expected for dates. However, qualitative estimates of amniotic fluid volume tend to be subjective. So if polyhydramnios is suspected, amniotic fluid should be assessed quantitatively using the AFI.

The volume of amniotic fluid cannot be safely measured directly, except perhaps during cesarean delivery. Thus, excessive fluid is defined indirectly using ultrasonographic criteria, typically the AFI. The AFI is the sum of the vertical depth of fluid measured in each quadrant of the uterus. The normal AFI ranges from > 5 to < 24 cm; values ≥ 24 cm indicate polyhydramnios.

Identification of cause

If polyhydramnios is present, further testing is recommended to determine the cause. Which tests are done may depend on which causes are suspected clinically (usually based on history or other ultrasound findings). Tests may include

  • Comprehensive ultrasonographic examination for fetal malformations (always recommended)

  • Maternal glucose challenge test

  • Kleihauer-Betke test (for fetomaternal hemorrhage)

  • Maternal serologic tests (eg, for syphilis, parvovirus, cytomegalovirus, toxoplasmosis, and rubella)

  • Amniocentesis and fetal karyotyping

  • Tests for clinically suspected hereditary disorders, such as anemias


  • Delivery at about 39 weeks

  • Possibly manual withdrawal of amniotic fluid (amnioreduction)

Recommendations for prenatal monitoring depend on the severity of polyhydramnios, based on AFI:

  • AFI ≥ 30 cm (which increases risk of fetal death): Prenatal monitoring should begin as early as 32 weeks or whenever it is diagnosed thereafter; it should include nonstress testing at least once a week. However, such monitoring has not been proved to decrease the fetal death rate.

  • AFI ≥ 24 to < 30 cm: Prenatal monitoring with nonstress testing is no longer recommended (1).

  • All degrees of polyhydramnios: Ultrasonography should be done every 4 weeks to check for macrosomia and to evaluate fetal anatomy.

Delivery at about 39 weeks should be planned. Mode of delivery should be based on the usual obstetrical indications (eg, presenting part).

Reducing amniotic fluid volume (eg, by amnioreduction) or reducing its production should be considered only if preterm labor occurs or if polyhydramnios causes severe maternal symptoms; however, there is no evidence that this approach improves outcomes. Also, there is no consensus on how much fluid to remove and how rapidly it should be removed, although removal of about 1 L over 20 minutes has been suggested.

Disorders that could be contributing to polyhydramnios (eg, maternal diabetes) should be controlled.

Treament reference

Key Points

  • Polyhydramnios can be caused by fetal malformations, multiple gestation, maternal diabetes, and various fetal disorders.

  • It is associated with increased risk of preterm contractions, premature rupture of membranes, maternal respiratory compromise, fetal malposition or death, and various problems during labor and delivery.

  • If polyhydramnios is suspected, determine amniotic fluid index and test for possible causes (including a comprehensive ultrasonographic evaluation).

  • Consider reducing amniotic fluid volume only if preterm labor occurs or if polyhydramnios causes severe symptoms.

  • Begin prenatal monitoring with weekly nonstress tests as early as 32 weeks in patients with an amniotic fluid index of ≥ 30 cm.

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NOTE: This is the Professional Version. CONSUMERS: Click here for the Consumer Version
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