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Oligohydramnios

By

Antonette T. Dulay

, MD, Main Line Health System

Last review/revision Oct 2022
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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:

Complications

Complications of oligohydramnios include the following:

  • Fetal death

  • 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

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

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 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 amniotic fluid index (AFI) or single deepest pocket (SDP).

The volume of amniotic fluid cannot be measured directly. Thus, excessive 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.

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, 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.

Treatment of Oligohydramnios

  • Serial ultrasonography to determine AFI and monitor fetal growth

  • Nonstress testing or biophysical profile

Ultrasonography should be done at least once every 2 to 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 Fetal Monitoring Labor consists of a series of rhythmic, involuntary or medically induced contractions of the uterus that result in effacement (thinning and shortening) and dilation of the uterine cervix. The... read more with nonstress testing or biophysical profile at least once a week and delivery at 36 to 37 weeks/6 days for isolated and uncomplicated oligohydramnios or at diagnosis if diagnosed at ≥ 37 weeks (1 Treatment reference 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... read more ). 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

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).

  • Do ultrasonography a least once every 4 weeks, and consider fetal monitoring at least once a week and delivery at 36 to 37 weeks/6 days or at diagnosis if diagnosed at ≥ 37 weeks (although optimal time for delivery varies based on clinical context).

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