1% live births

25% all congenital defects

90% unknown aetiology

10% alcohol, rubella, downs, drugs, diabetes, vitamin deficiency

defective embryogenesis

occur during 3-8 weeks gestation

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Normal Foetal Circulation

Non-functional lungs → umbilical veins → NORMAL shunt right to left via

  1. Ductus arteriosus (PDA)
  2. Foramen ovale (ASD)
  3. Ductus venosus (liver)