Duodenal atresia is a birth defect that causes an intestinal obstruction. It occurs in about 1 in 5,000 births, more commonly in boys. There are two main types - complete atresia where the duodenum is completely blocked, and incomplete atresia where the blockage is partial. Symptoms include vomiting of greenish fluid due to the inability to pass stomach contents further along the digestive tract, as well as abdominal distension. The diagnosis can be confirmed through medical imaging and tests.