Ultrasound cannot diagnose Down syndrome, or exclude it. However, if certain abnormalities are seen, suspicion for Down syndrome is increased. The most common is called A-V Canal, or Endocardial Cushion Defect. While it can be repaired, some infants will have severe problems. These relate to obstructive lesions of the intestine and esophagus.
Duodenal atresia is the most common, and is a blockage in the duodenum.
This can be corrected after birth, but may cause excess amniotic fluid, predisposing to premature labor. Another lesion is esophageal atresia, where the esophagus is blocked. This is characterized by a failure to see the normal fluid-filled stomach in ultrasound, as the fetus cannot swallow fluid into the stomach. Depending on the extent of the blockage, surgical repair can be relatively straightforward or difficult. These three findings are loosely associated with Down syndrome, and are seen in many normal fetuses.