Pyloric Stenosis (HPS)


What is pyloric stenosis?

Pyloric stenosis is a thickening or narrowing of the pylorus, a muscle in the stomach. This problem happens to newborns. The full name of the condition is hypertrophic pyloric stenosis (HPS). Hypertrophy means thickening. Pyloric stenosis causes projectile vomiting and can lead to dehydration in babies.

What happens in pyloric stenosis?

The pylorus is a muscular sphincter (muscle that opens and closes). It’s located at the end of the stomach, where the stomach meets the small intestine.

The pylorus contracts (closes) when food and liquid need to get digested in the stomach. It then relaxes (opens) to let food and liquid pass into the small intestine.

When the pyloric muscle is too thick, it narrows the passageway. Liquid and food can’t move from the stomach to the small intestine. Babies with pyloric stenosis often forcefully vomit since formula or breast milk can’t leave the stomach. Many babies have difficulty gaining weight because they have many episodes of vomiting.

Who is at risk for pyloric stenosis?

Risk factors for pyloric stenosis include:

  • Sex of the baby: Full-term, first-born male babies are at higher risk. It’s less likely in baby girls.
  • Race: It happens more to white infants, especially of European descent.
  • Family history of pyloric stenosis: About 15% of infants with pyloric stenosis have a family history of it. The parent who had the condition before also matters. An infant’s risk is three times higher if the mother had pyloric stenosis, compared to the father.
  • Smoking: Babies whose mothers smoked during pregnancy are at higher risk.
  • Antibiotics: Some babies who needed antibiotics shortly after birth may be at higher risk. Babies whose mothers took certain antibiotics late in pregnancy may also have a higher risk.
  • Approach to feeding: Some studies of babies drinking formula show an increased risk for pyloric stenosis. But it remains unclear if the risk comes from the bottle or the formula. If it comes from the bottle, it may also apply to bottles with breast milk.

When does pyloric stenosis occur?

Babies usually aren’t born with pyloric stenosis. The thickening of the pylorus starts to happen in the weeks after birth.

Pyloric stenosis symptoms usually start when the baby is 2 to 8 weeks old. But it can take up to five months for the symptoms to become apparent. If you notice symptoms, talk to your healthcare provider. It’s best to treat HPS before your baby becomes dehydrated and undernourished.

Can older children get pyloric stenosis?

In rare cases, older children can get a pyloric obstruction — something blocking the passage through the pylorus. Usually, a peptic ulcer is the cause in older children. Or perhaps a child has a rare disorder such as eosinophilic gastroenteritis, which inflames the stomach.

How common is pyloric stenosis?

Pyloric stenosis affects 3 out of every 1,000 babies born. It’s the most frequent condition requiring surgery in infants.

Symptoms and Causes

What are the symptoms of pyloric stenosis?

Symptoms start when babies are around 2 to 8 weeks old. Infants with pyloric stenosis may eat well but have these symptoms:

  • Frequent projectile vomiting (forceful vomiting), usually within a half hour to an hour after eating.
  • Abdominal (belly) pain.
  • Dehydration.
  • Hunger after feedings.
  • Irritability.
  • Small stools.
  • Wave-like stomach motion right after eating, just before vomiting starts. Occasionally a mass like a sausage can be felt in the stomach.
  • Weight loss.

Most babies appear otherwise healthy. Parents may not notice something is wrong until babies get very dehydrated or undernourished. Babies may also start to get jaundice, when the skin and whites of the eyes become yellow.

Is spit-up a sign of pyloric stenosis?

Many babies spit up a little after they eat. These dribbles are common and usually nothing to worry about. Forceful or painful projectile vomiting is a sign of a more serious issue. Talk to your healthcare provider if your child vomits after eating.

Diagnosis and Tests

How is pyloric stenosis diagnosed?

Your healthcare provider will ask you about your child’s eating habits. Then your child will get examined. Sometimes, providers can feel an olive-sized lump in your child’s belly. That’s the thickened pyloric muscle.

Your provider may recommend a blood test as well. This test can tell if your child is dehydrated or has an electrolyte imbalance from vomiting. Electrolytes are minerals that keep the body working the way it should.

What tests might my child need to diagnose pyloric stenosis?

If the provider doesn’t feel the lump or wants to confirm the diagnosis, your child may need an abdominal ultrasound. During this painless procedure:

  1. Your provider places a probe (tool) gently against the belly.
  2. The probe uses sound waves to create images.
  3. Your provider can often see the thickened pyloric muscle in the images.

Sometimes, even a physical exam and ultrasound don’t show any problems. If this happens, your provider may recommend an upper gastrointestinal (GI) series:

  1. Your child drinks a special liquid.
  2. The provider can see the liquid on an X-ray as it travels through the stomach toward the small intestine.
  3. Your provider can figure out if the liquid moves from the stomach through the pylorus. If it doesn’t, that indicates pyloric stenosis.

In some cases, an upper gastrointestinal series must be done if the physical exam and abdominal ultrasound do not reveal any abnormalities. This test requires that your child drink a special liquid. This liquid can be seen on an X-ray as it travels through the stomach and small intestine. The pediatric radiologist will be viewing the X-ray while your child drinks the liquid to determine whether or not the liquid is able to move out of the stomach through the pylorus.

Management and Treatment

What is pyloric stenosis treatment?

Surgery called pyloromyotomy treats pyloric stenosis. After diagnosing pyloric stenosis, your surgeon will discuss the surgery with you. It’s a safe surgery.

What happens before pyloric stenosis surgery?

Infants with pyloric stenosis often have dehydration because they vomit so much. Your provider will make sure your baby is properly hydrated before performing surgery. Your baby will probably need fluids through an IV which will be given at the hospital. A blood test to test hydration may be taken during this time to make sure it’s improving.

Your child won’t be able to have milk or formula starting six hours before surgery. Keeping them off these fluids reduces the risk of vomiting and aspiration (breathing in vomit) while under anesthesia.

What happens during pyloric stenosis surgery?

During pyloric stenosis surgery, the team will:

  1. Give your child general anesthesia. Your child will be asleep during the surgery and not feel any pain.
  2. Make a small incision (cut) on the left side of the abdomen, higher than the belly button.
  3. Perform a pyloromyotomy, making an incision in the thickened pylorus. This procedure allows food and liquid to travel from the stomach to the intestines.

How long is pyloric stenosis surgery?

The procedure usually takes less than an hour.

Can my child eat after pyloric stenosis surgery?

Your child will likely need to stay in the hospital for one to three days after surgery. Here’s what you can expect:

  • Your child will start eating formula or breast milk a few hours after surgery. They’ll eat small amounts at first. Your surgeon will discuss your child’s feeding plan with you.
  • If you use formula, the team will slowly increase the volume and concentration of the formula as your child can tolerate it.
  • If you breastfeed, your child will have breast milk from a bottle for the first few feedings. It’s important to accurately measure the amount.

What if my child still vomits after surgery?

Babies can still vomit after pyloric stenosis surgery. It doesn’t mean they have the condition again. Vomiting may be because of:

  • Anesthesia from the surgery.
  • Lack of adequate burping after feedings.
  • Too much food, too quickly.

If your child continues to vomit a lot, they may need more tests. Your care team will continue to work to correct any vomiting problems.


Can I prevent pyloric stenosis in my baby?

There’s no way to prevent pyloric stenosis. If you know pyloric stenosis runs in your family, make sure to tell your healthcare provider. The provider can be on the lookout for any signs or symptoms of the condition.

Knowing the signs and symptoms of pyloric stenosis means you can get help as soon as possible. Getting treatment early helps prevent problems such as malnourishment and dehydration.

Outlook / Prognosis

What is the outlook for babies with pyloric stenosis surgery?

The outlook for babies with HPS is very good. Most children do not have long-term problems after successful pyloric stenosis surgery. They eat well, grow and thrive.

Will my baby need a second pyloric stenosis surgery?

In rare cases, the pylorus is still too narrow after surgery. Surgeons may perform a second operation to cut it more.

Living With

How do I care for my child after pyloric stenosis surgery?

When you go home from the hospital:

  • Your child will be eating normally, so you can feed them without a problem.
  • Use medication such as acetaminophen (Tylenol®) if your child experiences any pain.
  • Give your child a sponge bath the day after surgery. At three days post-surgery, you can bathe them in the tub.
  • A small tape covers the incision, called a Steri-Strip™. Don’t pull it off yourself — it will fall off on its own. If it doesn’t, your provider will remove it at the follow-up appointment.

What happens at the follow-up appointment after pyloric stenosis surgery?

Bring your baby back to the provider around seven to 10 days after surgery. The provider will examine the surgical area and see how your child is recovering.

Are there activity restrictions after pyloric stenosis surgery?

Your child can go back to all regular activities. They can continue to have tummy time as well.

When should I call the healthcare provider?

Some normal swelling around the incision site is normal. But call your provider if your child has:

  • Bleeding.
  • Distended (swollen) or enlarged stomach.
  • Excessive swelling around the surgical area.
  • Fever.
  • Fewer wet diapers than usual.
  • Frequent vomiting.
  • Vomiting that appears dark green or contains blood.
  • Increased pain.
  • Redness or drainage (leaking) from the incision.

A note from Cleveland Clinic

Contact your healthcare provider if your baby has frequent projectile vomiting. Your baby may have a thickened muscle at the end of the stomach. This condition, pyloric stenosis, makes it hard for food and liquid to pass through. Babies may then vomit and become dehydrated or malnourished. Surgery for pyloric stenosis usually provides relief. Called pyloromyotomy, the treatment opens the muscle to restore the food’s path. Babies who receive this surgery have good outcomes, with few complications.

Last reviewed by a Cleveland Clinic medical professional on 11/19/2020.


  • Merck Manuals. Hypertrophic Pyloric Stenosis. ( Accessed 11/23/2020.
  • Healthy Children. American Academy of Pediatrics. Hypertrophic Pyloric Stenosis (HPS) — Help for Babies With Forceful Vomiting. ( Accessed 11/23/2020.
  • Pyloric Stenosis. ( Accessed 11/23/2020.

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