Refers to an abnormally large level of amniotic fluid; amniotic fluid index that is above the 95th centile for gestational age

Aetiology

• Idiopathic in 50-60% of cases
• Where an underlying abnormality can be identified, the most common causes include:
  • Any condition that prevents the foetus from swallowing e.g. oesophageal atresia, CNS abnormalities, muscular dystrophies, congenital diaphragmatic hernia
  • Duodenal atresia
  • Anaemia
  • Maternal diabetes
  • Macrosomnia
  • Twin-to-twin transfusion syndrome

Clinical features

Symptoms

• Abdominal discomfort
• Pre-labour rupture of membranes
• Preterm labour
• Cord prolapse

Signs

• LFD
• Malpresentation
• Tense shiny abdomen
• Inability to feel foetal parts

Investigations

• Ultrasound:
  • Amniotic fluid index (AFI) or maximum pool depth (MPD)
    • AFI > 25, DVP >8cm
  • Also assess foetal size, and foetal anatomy to detect any structural causes
• Maternal glucose tolerance test: for maternal diabetes
• Karyotyping: especially if other structural abnormalities are detected, or if the foetus is small
• TORCH screen