Pyloric stenosis

  • Pyloric stenosis (pie-lorr-ick sten-oh-sis) is a condition that affects the digestive system, which can cause your baby to vomit forcefully. It affects an estimated one in 500 babies.

    Food normally moves from the stomach to the small bowel via an opening called the pylorus. Pyloric stenosis happens when muscles around the pylorus become bigger and squeeze the opening, causing it to become narrow (stenosis). Food cannot empty out of the stomach because there is not enough room for it to pass through the pylorus into the bowel and it is often vomited out.

    Pyloric stenosis can lead to weight loss or poor weight gain from frequent vomiting, because the body cannot get the nutrients it needs from food. When the stenosis becomes severe, the vomiting becomes persistent and projectile (forceful), leaving babies at risk of severe dehydration.

    Pyloric stenosis happens in babies when they are between two and six weeks of age, and an operation is needed to fix the problem. It is more likely to happen in first-born male children of Caucasian families, particularly if a parent has had pyloric stenosis.

    Signs and symptoms of pyloric stenosis

    If your baby has pyloric stenosis, they may:

    • have persistent vomiting, which becomes progressively more forceful and may be projectile (the vomiting is non-bilious, which means it is not bright green in colour)
    • often be hungry after vomiting
    • have weight loss or poor weight gain. 

    Some children with pyloric stenosis have a pylorus that can be felt under the skin above the belly button – it typically feels like an olive.

    Diarrhoea is not usually a symptom of pyloric stenosis.

    When to see a doctor

    Dehydration is a very serious risk, especially in young babies. If your baby has persistent vomiting, or you are worried that they may have pyloric stenosis, see your GP immediately.

    Treatment for pyloric stenosis

    Your baby will need to be admitted to hospital for blood tests and to have treatment for dehydration. This is done by putting an intravenous drip (IV drip) into their vein, which is used to give them fluids. At this stage they do not need to drink.

    Your baby may also need to have a tiny plastic tube inserted through their nose and down in to their stomach. Nurses will use this to remove the contents of the stomach to stop any vomiting.

    Once your baby is rehydrated and their blood tests show improvement, an operation called a pylorotomy is performed to fix the problem, which opens up the narrow pylorus.

    Your baby can usually start feeding within six hours of the operation, although some children will continue to vomit for several days.

    Once the problem has been repaired by surgery, it is unusual for pyloric stenosis to come back again.

    Key points to remember

    • Pyloric stenosis usually happens in infants aged between two and six weeks.
    • Symptoms include forceful vomiting, being hungry after vomiting and weight loss or poor weight gains.
    • If your baby has persistent vomiting, see your GP immediately.
    • An operation is needed to correct pyloric stenosis.

    For more information

    • See your GP, paediatrician or Maternal and Child Health Nurse.
    • Kids Health Info fact sheet: Reflux (GOR) and GORD

    Common questions our doctors are asked

    Will my child need any other tests?

    In addition to blood tests, your child may have an ultrasound performed, to look at the pylorus. This is a painless procedure that involves no radiation and is the usual test to check for pyloric stenosis. In some babies, the diagnosis is so clear that an ultrasound isn't necessary.

    Are there lifelong problems following pyloric stenosis?

    No. If the stenosis and dehydration were found and corrected without complication, then there are almost never any long-lasting effects following surgery.

    Developed by The Royal Children's Gastroenterology department. We acknowledge the input of RCH consumers and carers.

    Reviewed May 2018.

    This information is awaiting routine review. Please always seek the most recent advice from a registered and practising clinician.

    Kids Health Info is supported by The Royal Children’s Hospital Foundation. To donate, visit


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