Causes of oligohydramnios include the following:
Uteroplacental insufficiency (eg, due to preeclampsia Preeclampsia and Eclampsia Preeclampsia is new-onset or worsening of existing hypertension with proteinuria after 20 weeks gestation. Eclampsia is unexplained generalized seizures in patients with preeclampsia. Diagnosis... read more , chronic hypertension Hypertension in Pregnancy Recommendations regarding classification, diagnosis, and management of hypertensive disorders (including preeclampsia) are available from the American College of Obstetricians and Gynecologists... read more , abruptio placentae Abruptio Placentae Abruptio placentae is premature separation of a normally implanted placenta from the uterus, usually after 20 weeks gestation. It can be an obstetric emergency. Manifestations may include vaginal... read more , a thrombotic disorder Thromboembolic Disorders in Pregnancy In the US, thromboembolic disorders—deep venous thrombosis (DVT) or pulmonary embolism (PE)—are a leading cause of maternal mortality. During pregnancy, risk is increased because Venous capacitance... read more , or another maternal disorder)
Drugs (eg, angiotensin-converting enzyme [ACE] inhibitors, nonsteroidal anti-inflammatory drugs [NSAIDs])
Fetal malformations, particularly those that decrease urine production
Fetal death
Idiopathic
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 dates.
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).
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 of Oligohydramnios
Serial ultrasonography to determine AFI and monitor fetal growth
Nonstress testing or biophysical profile
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 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 if oligohydramnios is isolated and uncomplicated (1 Treatment reference 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... 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
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
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 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 term (although optimal time for delivery varies).
