Neonatal Intestinal Obstruction

You are asked to evaluate a 12-hour-old newborn male infant because of bilious vomiting. Polydramnios and a dilated stomach were noted on serial prenatal ultrasounds, but amniocentesis was not performed. The infant was born at 36 weeks by vaginal delivery to a 35-year-old mother without complication. The infant has been irritable and has vomited dark-green bilious material with each of two attempts at feeding. The infant is noted on examination to have findings consistent with trisomy 21 (Down syndrome) including poor muscle tone, oblique palpebral fissures, epicanthal folds, and abnormally shaped ears. The abdominal examination shows epigastric prominence, but it is otherwise normal, and the anus is in a normal position and appears patent. Duodenal atresia is suspected.