Pyloric stenosis

Pyloric stenosis occurs when the passage between the stomach and small bowel (known as the “pylorus”) narrows. This is because the passage is made up of muscle which becomes thicker than normal, making the pylorus smaller and preventing the stomach from moving milk and food into the small intestine. It most often occurs in babies between two and six weeks of age. It’s not clearly known why pyloric stenosis develops but it is more common in boys than girls.

Signs and symptoms

  • Vomiting after feeding. The vomiting becomes worse over a few days and can often be forceful and projectile.
  • Baby often shows signs of hunger and wants to feed again after vomiting.
  • Weight loss or poor weight gain.
  • Possible decrease in the number of nappies with poo, as very little food is reaching the bowel.
  • Dehydration can develop quickly as the vomiting worsens. The baby can become lethargic, less active and their “soft spot” (fontanelle) on the top of their head can become sunken. They can have fewer wet nappies and when they cry, may not be able to make any tears.

Dehydration in young babies is a very serious condition. If your baby has persistent vomiting, you should see your doctor immediately.

Diarrhoea is NOT usually a symptom of pyloric stenosis.

How is the pyloric stenosis diagnosed?

The doctor will take a full history from you about your baby’s feeding pattern and weight. Sometimes, during physical examination of your baby, the doctor can feel a small hard lump on the right side of your baby’s stomach. They may refer your baby for an ultrasound of the stomach area (this is similar to the ultrasound that you may have had during pregnancy). This will give the doctor some pictures of the thickened pyloric muscle.


One of the complications of pyloric stenosis is vomiting and dehydration which can lead to changes in your baby’s blood salts (known as electrolytes). When your baby is admitted to hospital, they will have an intravenous drip (IV) inserted and have frequent blood tests (generally by pricking the heel) to make sure the electrolyte levels are stable. Your baby will also have fluid by the IV drip. At this stage, your baby won’t be allowed to have a breast feed or bottle in order to help control the vomiting. The IV fluid will be helping to rehydrate your baby. If your baby continues to vomit, the nurses may put a small tube (nasogastric tube) into their nose which then goes down to the stomach. The nurses can use this tube to remove any contents of the stomach by either drawing it out with a syringe (this is called aspirating) or by allowing it to drain itself into a small container (this is called free drainage).

Once your baby is rehydrated and the blood electrolytes are normal, an operation known as a “pyloromyotomy” will be performed under a general anaesthetic. There are no alternatives to surgery to fix pyloric stenosis. Both the surgeon and the anaesthetist will talk to you about the surgery and any risks or possible complications.

Once your baby has had surgery, they will return to the ward. The nurses will closely monitor your baby’s pain, wound and IV fluids. After six hours or so, your baby will start to feed with small amounts which will be increased slowly depending on how your baby tolerates it. Some babies continue to have small vomits after the operation but as the stomach heals, the vomiting should reduce and they should start feeding normally again. Once your baby is feeding well, you will be able to be discharged home, usually two to three days after the surgery.

Care at home

Your baby may still experience some pain from the surgery so ensure you have some pain relief available at home (such as liquid paracetomol). Dressing your baby in loose clothing may also help. The stitches used by the doctor during the surgery will dissolve so you won’t need to come back to have them removed. Your baby can have a shallow bath but try to keep the wound and dressing area dry for a few days after surgery to allow time for the wound to heal properly. Your surgeon will advise you as to whether or not you need to be seen at Queensland Children’s Hospital again or if you can see your family doctor (GP) for review after your baby has gone home.

When to get help

You should visit a GP if you have the following concerns:

  • your baby is in a lot of pain and pain relief does not seem to help
  • your baby is not feeding well and has signs of dehydration (dry nappies, lethargy, sunken soft spot)
  • your baby has a high temperature (37.50 C or higher) and paracetomol does not bring it down
  • the area around the operation site looks red or inflamed, is hot to touch or is oozing around the area
  • your baby continues to vomit and bring up milk and is not gaining weight.

In an emergency, call Triple Zero (000) and ask for an ambulance.

If you're not sure whether to go to an emergency department, call 13 HEALTH (13 43 25 84) and speak to a registered nurse.

Developed by Division of Medicine (Babies and General Paediatrics), Queensland Children’s Hospital. We acknowledge the input of consumers and carers.

Resource ID: FS138. Reviewed: November 2016.

Disclaimer: This information has been produced by healthcare professionals as a guideline only and is intended to support, not replace, discussion with your child’s doctor or healthcare professionals. Information is updated regularly, so please check you are referring to the most recent version. Seek medical advice, as appropriate, for concerns regarding your child’s health.

Last updated: October 2023