Vomiting all or most of feedings on a repeated basis is the main symptom of pyloric stenosis. Vomiting usually begins between a few days after birth and 5 months of age. But if your baby was premature, the start of symptoms may be delayed.

Vomiting caused by pyloric stenosis usually starts gradually and gets worse over time. As the pylorus, the connection between your baby's stomach and intestine, becomes tighter, the vomiting becomes more frequent and more forceful (projectile vomiting). Your baby likely has a problem different from pyloric stenosis if his or her vomit is yellow or green.

A baby with pyloric stenosis:

• Vomits formula or breast milk shortly after a feeding.
• Has a full (distended) upper abdomen after a feeding.
• Acts irritable and hungry.
• Has fewer and harder stools (constipation) than normal.
• Passes smaller amounts of urine than normal.

As the vomiting continues, your baby will:

• Lose weight.
• Develop symptoms of not getting enough fluids (dehydration).
• Be sleepier than normal and very fussy when awake.

When to call a doctor

Call your doctor if your baby:

• Has vomited most or all of his or her feeding for two feedings in a row.
• Is vomiting yellow or green liquid (bile). This could indicate a problem more serious than pyloric stenosis.
• Has symptoms of dehydration.
• Is 5 months of age or younger and has symptoms of pyloric stenosis, such as repeated forceful vomiting shortly after feedings, irritability, hunger, and less urine.