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.

Epidemiology

The estimated prevalence can be up to ~6% of pregnancies ⁴.

Pathology

Causes

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
- premature rupture of membranes (PROM)
- preterm premature rupture of membranes (PPROM)
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

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