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.

Epidemiology

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

Pathology

Aetiology

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 (indometacin)

• R: renal abnormalities (from decreased urine output)

  • renal agenesis

  • renal dysplasia

  • posterior urethral valves

  • polycystic kidneys

  • multicystic dysplastic kidney (MCDK)

  • urethral atresia

• 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)

  • trisomy 18

  • trisomy 13

  • triploidy

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

See also

• polyhydramnios

• anhydramnios