Polyhydramnios is excessive amniotic fluid; it is associated with maternal and fetal complications. Diagnosis is by ultrasonographic measurement of amniotic fluid volume. Management is by treating maternal disorders contributing to polyhydramnios. 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:
Idiopathic
Fetal malformations (eg, gastrointestinal or urinary tract obstruction)
Fetal anemia, including hemolytic anemia due to hemolytic disease of the fetus and newborn
Other fetal disorders (eg, infections) or genetic abnormalities
Complications
With polyhydramnios, risk of the following complications is increased:
Preterm contractions and possibly prelabor rupture of membranes (sometimes followed by placental abruption) or preterm labor
Maternal respiratory compromise
Uterine atony
Fetal death (risk is increased even when polyhydramnios is idiopathic)
Risk of complications tends 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 of Polyhydramnios
Polyhydramnios is often asymptomatic. Sometimes the uterus is larger than expected for dates. Some women, especially when polyhydramnios is severe and causes uterine distention, have difficulty breathing and/or painful preterm contractions.
Diagnosis of Polyhydramnios
Ultrasonographic measurement of amniotic fluid volume
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 amniotic fluid index (AFI) or single deepest pocket (SDP).
AFI ≥ 24 cm: AFI is the sum of the vertical depth of fluid measured in each quadrant of the uterus; normal AFI ranges from > 5 to < 24 cm.
SDP ≥ 8 cm: SDP is a measurement of the deepest pocket of amniotic fluid; normal SDP is ≥ 2 to < 8 cm.
It appears that neither AFI nor SDP is superior to the other in terms of preventing adverse perinatal outcomes. Each has limitations: AFI often results in overdiagnosis of oligohydramnios; SDP results in overdiagnosis of polyhydramnios (1, 2).
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. The tests done 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
Amniocentesis and fetal karyotyping, if other ultrasound findings are present
Tests for clinically suspected hereditary disorders (eg, anemias), if the family history suggests risk
Diagnosis references
1. Kehl S, Schelkle A, Thomas A, et al: Single deepest vertical pocket or amniotic fluid index as evaluation test for predicting adverse pregnancy outcome (SAFE trial): A multicenter, open-label, randomized controlled trial. Ultrasound Obstet Gynecol 47 (6):674–679, 2016. doi: 10.1002/uog.14924
2. Nabhan AF, Abdelmoula YA: Amniotic fluid index versus single deepest vertical pocket as a screening test for preventing adverse pregnancy outcome. Cochrane Database Syst Rev 2008 (3):CD006593, 2008. doi:10.1002/14651858.CD006593.pub2
Treatment of Polyhydramnios
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 not 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 when AFI is ≥ 30 cm. 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 polyhydramnios causes severe maternal discomfort. Also, there is no consensus on how much fluid to remove and how rapidly it should be removed, although removal of approximately 1 L over 20 minutes has been suggested.
Disorders that could be contributing to polyhydramnios (eg, maternal diabetes) should be controlled.
Treament reference
1. Society for Maternal-Fetal Medicine (SMFM); Dashe JS, Pressman, EK, Hibbard JU: SMFM Consult Series #46: Evaluation and management of polyhydramnios. Am J Obstet Gynecol 219 (4):B2–B8, 2018. doi: 10.1016/j.ajog.2018.07.016
Key Points
Polyhydramnios is excessive amniotic fluid; it can be caused by fetal malformations, multiple gestation, maternal diabetes, and various fetal disorders.
It is associated with increased risk of preterm contractions, preterm labor, prelabor rupture of membranes, maternal respiratory compromise, fetal malposition or death, and various problems during labor and delivery.
If polyhydramnios is suspected, do ultrasonography to determine amniotic fluid index or single deepest pocket, and test for possible causes (including a comprehensive ultrasonographic evaluation).
Consider reducing amniotic fluid volume only if polyhydramnios causes severe maternal symptoms.
Begin prenatal monitoring with weekly nonstress tests as early as 32 weeks in patients with an amniotic fluid index of ≥ 30 cm.
