Causes of oligohydramnios include the following:
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Uteroplacental insufficiency (eg, due to preeclampsia, chronic hypertension, abruptio placentae, a thrombotic disorder, or another maternal disorder)
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Drugs (eg, angiotensin-converting enzyme [ACE] inhibitors, nonsteroidal anti-inflammatory drugs [NSAIDs])
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Fetal malformations, particularly those that decrease urine production
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Fetal death
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Fetal chromosomal abnormalities (eg, aneuploidy)
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Rupture of membranes (premature or at term)
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Idiopathic
Complications
Symptoms and Signs
Diagnosis
Oligohydramnios may be suspected if uterine size is less than expected for dates or if fetal movements are decreased; it may also be suspected 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).
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 ≤ 5 cm indicate oligohydramnios.
Identification of cause
If oligohydramnios is diagnosed, clinicians should check for possible causes, including premature rupture of membranes. Comprehensive ultrasonographic examination is done to check for fetal malformations and any evident placental causes (eg, abruptio placentae).
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.
Treatment
Ultrasonography should be done at least once every 4 weeks (every 2 weeks if growth is restricted) to monitor fetal growth. The AFI should be measured at least once a week. Most experts recommend fetal monitoring with nonstress testing or biophysical profile at least once a week and delivery at 36 to 37 weeks/6 days if oligohydramnios is isolated and uncomplicated (1). However, this approach has not been proved to prevent fetal death.
Also, optimal time for delivery is controversial and can vary based on patient characteristics and fetal complications.
Treatment reference
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1. American College of Obstetricians and Gynecologists (ACOG): ACOG Committee Opinion No. 764: Medically indicated late-preterm and early-term deliveries. Obstet Gynecol 133 (2):e151-e155, 2019. doi: 10.1097/AOG.0000000000003083
Key Points
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Oligohydramnios can be caused by uteroplacental insufficiency, drugs, fetal abnormalities, or rupture of membranes.
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It can cause problems in the fetus (eg, growth restriction, limb contractures, death, delayed lung maturation, inability to tolerate labor).
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If oligohydramnios is suspected, determine the amniotic fluid index and test for possible causes (including doing a comprehensive ultrasonographic evaluation).
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Do ultrasonography a least once every 4 weeks, and consider fetal monitoring at least once a week and delivery at term (although optimal time for delivery varies).
