An estimate of gestational age by ultrasonography improves the performance of the triple test.

Second-trimester ultrasound assessment may be helpful for predicting the likelihood of trisomy 21 in pregnancies at increased risk.

Ultrasonographic findings associated with fetal Down syndrome :

• Increased nuchal fold thickness >5 mm
  
  
• Intrauterine growth restriction
  
  
• Mild cerebral ventriculomegaly
  
  
• Brachycephaly
  
  
• Flat facies
  
  
• Small ears


• Choroid plexus cysts
  
  
• Cystic hygromas
  
  
• Echogenic intracardiac foci
  
  
• Congenital heart defects
  
  

  • ventricular septal defect
  • Atrio-ventricular canal
  • Tetralogy of Fallot
  • Bright papillary muscle
  
  
  
• Increased intestinal echogenicity
  
  
• Duodenal atresia ("double -bubble sign") after 22 weeks' gestation
  
  
• Renal pelvis dilation
  
  
• Shortened humerus and femur
  
  
• Increased iliac wing angle
  
  
• Incurving (clinodactyly) and hypoplasia of the fifth finger
  
  
• Increased space between first and second toes
  
  
• Two-vessel umbilical cord
  
  
• Nonimmune hydrops
  
  
• Possible increased biparietal diameter-femur length ratio