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Oligohydramnios

By Antonette T. Dulay, MD, Attending Physician, Maternal-Fetal Medicine Section, Department of Obstetrics and Gynecology;Senior Physician, Main Line Health System;Axia Women’s Health

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Oligohydramnios is a deficient volume of amniotic fluid; it is associated with maternal and fetal complications. Diagnosis is by ultrasonographic measurement of amniotic fluid volume. Management involves close monitoring and serial ultrasonographic assessments.

The volume of amniotic fluid cannot be safely measured directly, except perhaps during cesarean delivery. Thus, deficient fluid is defined indirectly using ultrasonographic criteria, typically the amniotic fluid index (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.

Causes of oligohydramnios include the following:

Complications

Complications of oligohydramnios include the following:

  • Fetal death

  • Intrauterine growth restriction

  • Limb contractures (if oligohydramnios begins early in the pregnancy)

  • Delayed lung maturation (if oligohydramnios begins early in the pregnancy)

  • Inability of the fetus to tolerate labor, leading to the need for cesarean delivery

Risk of complications depends on how much amniotic fluid is present and what the cause is.

Symptoms and Signs

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 dates. Disorders causing or contributing to oligohydramnios may cause symptoms.

Diagnosis

  • Ultrasonographic measurement of amniotic fluid volume

  • Comprehensive ultrasonographic 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 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 AFI.

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

  • Serial ultrasonography to determine AFI and monitor fetal growth

  • Nonstress testing or biophysical profile

Ultrasonography should be done at least once every 4 wk (every 2 wk if growth is restricted) to monitor fetal growth. The AFI should be measured at least once/wk. Most experts recommend fetal monitoring with nonstress testing or biophysical profile at least once/wk and delivery at term. 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.

Key Points

  • Oligohydramnios can be caused by uteroplacental insufficiency, drugs, fetal abnormalities, or premature 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 and test for possible causes (including doing a comprehensive ultrasonographic evaluation).

  • Do ultrasonography a least once every 4 wk, and consider fetal monitoring at least once/wk and delivery at term (although optimal time for delivery varies).