Oligohydramnios

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

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)
  • 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