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.
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Epidemiology
The estimated prevalence can be up to ~6% of pregnancies 4.
Pathology
Etiology
The causes of oligohydramnios are protean and one way to simplify them is by using the mnemonic DRIPPC:
-
D:
- demise
- drugs: e.g. prostaglandin inhibitors (indomethacin)
- R: renal abnormalities (from decreased urine output)
- I: IUGR (intra-uterine growth restriction): 80% may occur from decreased renal perfusion due to sparing effect
- P: premature rupture of membranes
- P: post dates
- C: chromosomal anomalies (especially if other anomalies are found)
Associations
- Potter sequence
- underlying fetal hypoxia and fetal cardiovascular compromise: from preferential flow to the fetal brain at the expense of diminished renal blood flow
- twin pregnancy-related complications:
- twin to twin transfusion syndrome: in pump twin
- maternal dehydration
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
- maximum vertical pocket depth: <2 cm
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
- first-trimester oligohydramnios can result in failure of pregnancy in up to 95% from complications such as
- pulmonary hypoplasia: implies a very poor prognosis
- fetal limb contractures
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