A 2-day-old neonatal male born 39 weeks’ gestation is evaluated by the pediatrician for recurrent episodes of bilious vomiting after feeds. Physical examination shows a slightly distended abdomen. No other abnormalities are noted. Which of the following is the most appropriate next step in diagnosis?
Abdominal ultrasound
Abdominal x-ray
Enema
lnsertion of nasogastric tube
Upper GI series
