30th April 2024

A 5-week-old male infant presents with a two-week history of progressively worsening projectile vomiting after feeding.

A 5-week-old male infant presents with a two-week history of progressively worsening projectile vomiting after feeding. The vomiting is non-bilious, and the infant appears hungry and irritable after episodes. The mother reports that the infant’s weight gain has plateaued despite a good appetite. On examination, the infant appears dehydrated but otherwise healthy. There is no abdominal distention or palpable mass.

Which investigation is most appropriate to confirm the diagnosis of pyloric stenosis?