Oligohydramnios refers to a situation where the amniotic fluid volume is less than expected for gestational age. Often these fetuses have <500 mL of amniotic fluid. When there is almost no amniotic fluid present, this is termed anhydramnios.
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Epidemiology
The estimated prevalence can be up to ~6% of pregnancies 4.
Associations
underlying fetal hypoxia and fetal cardiovascular compromise: from preferential flow to the fetal brain at the expense of diminished renal blood flow
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twin pregnancy-related complications:
twin to twin transfusion syndrome: in pump twin
maternal dehydration
Pathology
Etiology
The causes of oligohydramnios are protean and one way to simplify them is by using the mnemonic DRIPPC:
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D:
drugs: e.g. prostaglandin inhibitors (indomethacin)
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R: renal abnormalities (from decreased urine output)
I: IUGR (intra-uterine growth restriction): 80% may occur from decreased renal perfusion due to sparing effect
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P: premature rupture of membranes
P: post dates
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C: chromosomal anomalies (especially if other anomalies are found)
Radiographic features
Antenatal ultrasound
Several sonographic criteria can be used which include:
four quadrants amniotic fluid index (AFI): <5 cm
two diameter pocket method: <1 x 1 cm or <15 cm2
Treatment and prognosis
The development of oligohydramnios early in pregnancy is generally a poor prognostic marker. Amnio-infusion can be attempted in severe cases if appropriate.
Complications
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first-trimester oligohydramnios can result in failure of pregnancy in up to 95% from complications such as
pulmonary hypoplasia: implies a very poor prognosis
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