Oligohydramnios is amniotic fluid volume that is less than expected for gestational age; it is associated with maternal and fetal complications. Diagnosis is by ultrasonographic measurement of amniotic fluid volume. Management involves close fetal monitoring and serial ultrasonographic assessments.
Causes of oligohydramnios include the following:
Uteroplacental insufficiency (eg, due to preeclampsia, chronic hypertension, placental abruption, a thrombotic disorder, or another maternal disorder)
Rupture of membranes (preterm or at term)
Some medications (eg, angiotensin-converting enzyme [ACE] inhibitors, nonsteroidal anti-inflammatory drugs [NSAIDs])
Fetal chromosomal abnormalities (eg, aneuploidy)
Fetal malformations, particularly those that decrease urine production
Fetal death
Idiopathic
Complications
Complications of oligohydramnios include the following:
Intrauterine growth restriction
Limb contractures (if oligohydramnios begins early in the pregnancy)
Delayed or incomplete lung maturation (if oligohydramnios begins early in the pregnancy)
Inability of the fetus to tolerate labor, leading to the need for cesarean delivery
Fetal death
Risk of complications depends on how much amniotic fluid is present and the etiology.
Symptoms and Signs of Oligohydramnios
Oligohydramnios itself tends not to cause maternal symptoms other than a sense of decreased fetal movement. Uterine size may be less than expected based on gestational age.
Disorders causing or contributing to oligohydramnios may cause symptoms.
Diagnosis of Oligohydramnios
Ultrasonographic measurement of amniotic fluid volume
Comprehensive ultrasonographic fetal examination, including evaluation for fetal malformations
Testing for clinically suspected maternal causes
Oligohydramnios may be suspected if uterine size is less than expected for dates or if fetal movements are decreased; it may also be detected based on incidental ultrasonographic findings. However, qualitative estimates of amniotic fluid volume tend to be subjective. If oligohydramnios is suspected, amniotic fluid should be assessed quantitatively using the amniotic fluid index (AFI) or single deepest pocket (SDP).
The volume of amniotic fluid cannot be measured directly. Thus, low fluid is defined indirectly using one of the following ultrasonographic criteria:
AFI ≤ 5 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 < 2 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).
Identification of cause
If oligohydramnios is diagnosed, clinicians should check for possible causes, including prelabor rupture of membranes. Comprehensive ultrasonographic examination is done to check for fetal malformations and any evident placental causes (eg, placental abruption).
Clinicians can offer amniocentesis and fetal karyotyping if ultrasonography suggests fetal malformations or aneuploidy.
If uteroplacental insufficiency is suspected and intrauterine growth restriction is detected, the umbilical artery is assessed using Doppler ultrasonography.
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 Oligohydramnios
Serial ultrasonography to determine amniotic fluid index (AFI) or single deepest pocket (SDP) and monitor fetal growth
Nonstress testing or biophysical profile
Patients may be managed as inpatients. If they are managed as outpatients, fetal status should be monitored once or twice a week with ultrasound measurement of AFI or SDP and a nonstress test or biophysical profile (1). Ultrasonography to measure fetal growth should be done every 2 to 4 weeks (every 2 weeks if growth is restricted).
Most experts recommend delivery as early as 36 to 37 6/7 weeks for isolated and uncomplicated oligohydramnios or at diagnosis if diagnosed at ≥ 37 weeks (2). However, this approach has not been proven to prevent fetal death. Optimal time for delivery is controversial and can vary based on patient characteristics and fetal complications.
Treatment references
1. American College of Obstetricians and Gynecologists (ACOG): ACOG Committee Opinion, Number 828: Indications for Outpatient Antenatal Fetal Surveillance. Obstet Gynecol. 2021;137(6):e177-e197. doi:10.1097/AOG.0000000000004407
2. American College of Obstetricians and Gynecologists’ Committee on Obstetric Practice, Society for Maternal-Fetal Medicine: Medically indicated late-preterm and early-term deliveries: ACOG Committee Opinion, Number 831. Obstet Gynecol 138 (1):e35–e39, 2021. doi: 10.1097/AOG.0000000000004447
Key Points
Oligohydramnios is amniotic fluid volume that is less than expected for gestational age.
Oligohydramnios can be caused by uteroplacental insufficiency, drugs, fetal abnormalities, or rupture of membranes.
It can cause problems in the fetus (eg, growth restriction, limb contractures, death, delayed lung maturation, inability to tolerate labor).
If oligohydramnios is suspected, determine the amniotic fluid index or single deepest pocket and test for possible causes (including doing a comprehensive ultrasonographic evaluation).
Admit to the hospital for monitoring, or if managed as an outpatient, monitor AFI or SDP and do a nonstress test or biophysical profile once or twice a week. Measure fetal growth with ultrasonography every 2 to 4 weeks.
Most experts recommend delivery as early as 36 to 37 6/7 weeks or at diagnosis if diagnosed at ≥ 37 weeks (although optimal time for delivery varies based on clinical context).
