A 4 week old male infant presents with 12 episodes of vomiting over 4 days, which progressively worsened over time and became projectile in nature. No bile or blood was present.

He is always hungry and often vomits after feeds. He has been exclusively breastfed so far.

He was born at term with a birth weight of 3.6kg, which is between the 50th to 75th centiles.