Pyloric Stenosis

Pyloric Stenosis

Pyloric stenosis is a condition where milk cannot get out of the stomach because the 'exit' is extremely narrow.

Images used with permission of Mayo Foundation for Medical Education and Research, all rights reserved.

Images showing how Pylorus stenosis affects the stomach


Key points to remember about pyloric stenosis

  • the pylorus is the passage that connects the lower part of the stomach to the rest of the bowel
  • all food leaving the stomach has to go through the pylorus
  • when a baby has pyloric stenosis, the muscles in the pylorus have become too thick to allow milk to pass through it
  • the first symptom is usually forceful, or projectile vomiting soon after feeds
  • if your baby has pyloric stenosis, they will need surgery
  • your baby's dehydration may need treatment with intravenous fluids before surgery

What is pyloric stenosis?

Pyloric stenosis (also called infantile hypertrophic pyloric stenosis) is a narrowing of the pylorus - the passage leading from the stomach to the small intestine. When a baby has pyloric stenosis, the muscles in the pylorus have become too thick to allow milk to pass through it. This usually happens in the first 6 weeks after birth.

What causes pyloric stenosis?

Experts do not know exactly what causes the thickening and enlargement of the muscles in the pylorus.

What puts my baby at risk of getting pyloric stenosis?

Pyloric stenosis affects far more boys than girls and tends to run in families.

What are the signs and symptoms of pyloric stenosis in babies?


  • vomiting of feeds, usually within 30 minutes of a feed
  • vomiting tends to get worse until your baby is vomiting after every feed 
  • vomiting may be so forceful that the vomit can be projected 1 metre out of the mouth (projectile vomiting)
  • the vomit is usually yellow, the colour of curdled milk
  • occasionally, the vomit may have small brown specks of old blood in it
  • despite the vomiting, babies are usually keen to feed (because they are starving)

Weight loss

  • failure to gain weight or weight loss

Being miserable

  • because they remain hungry
  • from stomach cramps which may be painful


  • dry mouth and tongue
  • fewer wet nappies or not doing as much wee as usual
  • unusual sleepiness, difficult to rouse (lethargic)
  • sunken eyes
  • the soft spot on the top of the head (fontanelle) is more sunken than normal


  • sometimes you can see ripples or waves move across the stomach (abdomen) after a feed - these are muscle contractions (peristalsis) as the stomach tries to empty into the small intestine

Less poo

  • less poo - and poos can be smaller 

When should I seek help for my baby with pyloric stenosis?

If you think your child has pyloric stenosis, go to your doctor or after-hours medical centre straightaway. Do not delay as young babies who are not able to feed normally can become more ill very quickly.

How is pyloric stenosis diagnosed?

Your doctor will ask about your baby's symptoms, including:

  • patterns of feeding and vomiting
  • the colour of the vomit
  • any weight loss or failure to gain weight

Your doctor may try to feel a mass or lump (which is the thickened pylorus) in your baby's stomach.

Your baby might need some investigations or tests. 

An ultrasound of your baby's abdomen

An ultrasound may show the thickened pyloric muscle.

A test feed

A doctor may give your child a small feed. This is to help your baby relax enough to allow the doctor to feel the lump in your child's tummy. 

A barium meal

This is a special x-ray. Only a very small number of babies need it. A doctor or nurse will give your baby a small amount of chalky liquid (barium). Your baby will then have an x-ray of their abdomen, which will show the passage of the barium through the gut. Any blockage or narrowing will show on the x-ray.

Blood tests

In most cases, your baby will need a blood test. 

What is the treatment for my baby with pyloric stenosis?

The treatment for pyloric stenosis is an operation called a pyloromyotomy.

A team that usually includes a surgeon and an anaesthetist will do this operation using one of 3 techniques:

  1. 'Key hole' surgery - the surgeon makes 3 three tiny cuts. This is the usual technique.
  2. Open operation - the surgeon makes a small cut directly over the pylorus.
  3. Umbilical approach - the surgeon makes a cut in the tummy button (umbilicus) itself.

In all the operations, the surgeon cuts through and spreads the thickened and enlarged muscles of the pylorus, which relieves the blockage (obstruction).

What happens to my baby before the operation for pyloric stenosis?


Ask you doctor or nurse about when and what your baby can drink before the operation. 


Your baby will need an intravenous drip before the operation. Babies with pyloric stenosis usually have abnormal levels of several important substances in their blood. These levels must return to normal before the operation. This usually takes several hours and can even take a day or two.

Talk with the surgical team

Your baby's surgical team will explain what will happen during the operation, and any other treatment needed. You will have the opportunity to ask questions.

What happens to my baby after the operation for pyloric stenosis?

Your baby may need medicine to help with pain after the operation. This may be through an intravenous drip.

For the first few hours, your baby will continue to have fluids through the drip. This will give the stomach time to start healing. Your baby will be able to start feeding after about 12 hours. You will have to start with small amounts.

Your baby may still vomit some of the feed, but this won't be forceful or projectile vomiting as before. The vomits or spills will decrease over several days. You will be able to take your baby home once they are feeding normally.

How can I care for my baby at home after treatment for pyloric stenosis?

Your baby may still be sore for a day or two once you go home. Your doctor will suggest medicines to help with pain after you leave the hospital. 

Handle your baby normally.

Usually, you can bath your baby any time after the surgery. Check this with your surgeon.

Keep an eye on the wound. Take your baby to your doctor straightaway if you notice any signs of infection:

  • redness around the wound
  • oozing or pus coming from the wound
  • swelling around the wound
  • your baby has a fever
  • your baby stops feeding

Are there any complications of treatment for pyloric stenosis?

There is some risk with any surgery - bleeding during and after the surgery and a small risk with having an anaesthetic. There is a small chance of damage to the delicate lining of the bowel, but the surgeon usually finds and fixes this during surgery. Pyloric stenosis can happen again, but this is rare.


Images used with permission of Mayo Foundation for Medical Education and Research, all rights reserved.

This page last reviewed 21 September 2020.

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