Causes of polyhydramnios include the following:
Fetal malformations (eg, gastrointestinal or urinary tract obstruction)
Fetal anemia, including hemolytic anemia due to Rh incompatibility Hemolytic Disease of the Fetus and Neonate Hemolytic disease of the fetus and neonate is hemolytic anemia in the fetus (or neonate, as erythroblastosis neonatorum) caused by transplacental transmission of maternal antibodies to fetal... read more
Other fetal disorders (eg, infections) or genetic abnormalities
Idiopathic
Complications
With polyhydramnios, risk of the following complications is increased:
Premature rupture of membranes Prelabor Rupture of Membranes (PROM) Prelabor rupture of membranes is leakage of amniotic fluid before onset of labor. Diagnosis is clinical. Delivery is recommended when gestational age is ≥ 34 weeks and is generally indicated... read more , sometimes followed by placental abruption Placental Abruption (Abruptio Placentae) Placental abruption (abruptio placentae) is premature separation of the placenta from the uterus, usually after 20 weeks gestation. It can be an obstetric emergency. Manifestations may include... read more
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 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 using one of the following ultrasonographic criteria:
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 Diagnosis references 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... read more , 2 Diagnosis references 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... read more ).
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
Maternal serologic tests (eg, for syphilis, parvovirus, cytomegalovirus, toxoplasmosis, and rubella)
Amniocentesis and fetal karyotyping
Tests for clinically suspected hereditary disorders, such as anemias
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.
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 recommended (1 Treament reference 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... read more ).
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
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 Epub 2018 Jul 23.
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, premature 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 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.
