Polyhydramnios

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 fetus 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 presentation

Symptoms

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

Signs

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

Investigations

Ultrasound

  • Amniotic fluid index (AFI) or maximum pool depth (MPD)
    • AFI > 25, DVP >8cm
  • Also:
    • Assess fetal size
    • Assess fetal anatomy to detect any structural causes

Others

  • Maternal glucose tolerance test - for maternal diabetes 
  • Karyotyping - especially if other structural abnormalities are detected, or if the fetus is small
  • TORCH screen
  • Antibody screen

Management

  • No medical intervention is required in the majority of women with polyhydramnios
  • If the maternal symptoms are severe (e.g. breathlessness), an aminoreduction can be considered
  • IOL by 40 weeks

Complications

  • Risks during labour include malpresentation, cord prolapse and PPH