Oligo- vs Poly- hydramnios

Oligohydramnios

• Definition: Too little amniotic fluid
  • AFI < 5 cm or Single Deepest Pocket < 2 cm
• Key Features:
  • Poor fetal movement (cord compression)
  • Potter sequence
  • ↑ Risk of complications: cord compression, fetal distress, pulmonary hypoplasia
• Common Causes:
  • Renal causes:
    • Bilateral renal agenesis
    • Posterior urethral valves
    • Polycystic kidney disease
  • Placental insufficiency:
    • IUGR
    • HTN, Pre-eclampsia, Abruptio placentae
  • Rupture of membranes (PROM/PPROM)
  • Post-term pregnancy
  • Certain medications:
    • ACE inhibitors
    • NSAIDs

Polyhydramnios

• Definition: Too much amniotic fluid
  • AFI > 24 cm or Single Deepest Pocket > 8 cm
• Key Features:
  • Maternal discomfort, preterm labor
  • Fetal malpresentation
  • Risk of cord prolapse during ROM
• Common Causes:
  • Fetal GI tract obstruction:
    • Esophageal atresia
    • Duodenal atresia
    • Anencephaly (↓ swallowing)
  • Fetal anemia (e.g., Parvovirus B19, alloimmunization)
  • Maternal diabetes (↑ fetal urination due to hyperglycemia)
  • Multiple gestation (esp. twin-twin transfusion syndrome)
  • Idiopathic (majority of cases)