Pyloric Stenosis (HPS)

Pyloric stenosis is a condition that affects your infant’s pylorus, the muscle at the end of the stomach leading to the small intestine. When their pylorus thickens and narrows, food can’t pass through. Pyloric stenosis symptoms include forceful vomiting, which may cause dehydration and malnourishment. Surgery can repair the problem.


A healthy pylorus (muscular opening between stomach and small intestine) and a pyloric stenosis.
Pyloric stenosis is the thickening and narrowing of your baby’s pylorus (the muscular opening between their stomach and their small intestine).

What is pyloric stenosis?

Pyloric stenosis is the thickening and narrowing of your baby’s pylorus, which is the muscular opening between their stomach and their small intestine. The full medical term for this condition is hypertrophic pyloric stenosis (HPS):

  • Hypertrophic refers to hypertrophy, which means thickening.
  • Pyloric refers to the pylorus.
  • Stenosis means narrowing.

HPS causes projectile vomiting and can lead to dehydration in babies. Fortunately, surgery can repair this issue.


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What happens in pyloric stenosis?

Your pylorus is a muscular sphincter (a muscle that opens and closes). It’s located at the end of your stomach, where your stomach meets your small intestine. Your pylorus contracts (closes) when your stomach is digesting food and liquid. It then relaxes (opens) to let food and liquid pass into your 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. A baby with pyloric stenosis often forcefully vomits since formula or breast milk can’t leave their stomach. Many babies have difficulty gaining weight because they have many episodes of vomiting.

How often do babies with pyloric stenosis vomit?

Babies with pyloric stenosis may vomit after every feeding or after just some feedings.

When does pyloric stenosis occur?

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

Pyloric stenosis symptoms usually start when your baby is between 3 and 6 weeks old. But it can take up to five months for symptoms to become apparent. If you notice symptoms, talk to your baby’s 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 their pylorus. Usually, a peptic ulcer is the cause in older children. Sometimes, a rare disorder such as eosinophilic gastroenteritis, which inflames the stomach, can cause the condition.

How common is pyloric stenosis?

Pyloric stenosis affects 1 to 3.5 out of every 1,000 newborns. It’s the most frequent condition requiring surgery in infants.

Symptoms and Causes

What are the symptoms of pyloric stenosis?

Pyloric stenosis symptoms typically start when your baby is between 3 and 6 weeks old. Infants with pyloric stenosis may eat well but have these symptoms:

  • Frequent projectile vomiting (forceful vomiting), usually within a half hour to one hour after eating.
  • Abdominal (belly) pain.
  • Dehydration.
  • Hunger after feedings.
  • Irritability.
  • Small poops (stools).
  • Wavelike stomach motion right after eating, just before vomiting starts. Occasionally, you can feel a mass like a sausage in your baby’s stomach.
  • Weight loss.

Most babies appear otherwise healthy. Parents may not notice something’s wrong until babies get very dehydrated or undernourished. Babies may also start to get jaundice, when the skin and whites of their 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 baby’s healthcare provider if your baby vomits after eating.


What causes pyloric stenosis?

Scientists don’t know the exact cause of pyloric stenosis. However, genetics and environmental factors may play a role.

What are the risk factors for pyloric stenosis?

Risk factors for pyloric stenosis include:

  • Family history: About 15% of infants with pyloric stenosis have a biological family history of the condition.
  • Sex: Full-term, firstborn babies assigned male at birth (AMAB) are at a higher risk. The condition is less common in babies assigned female at birth (AFAB).
  • Race: The condition is more common in white infants, especially those of European descent.
  • Smoking: Babies whose birthing parent smoked during pregnancy are at a higher risk.
  • Antibiotics: Some babies who needed antibiotics shortly after birth may be at a higher risk. Babies whose birthing parents 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.

Diagnosis and Tests

How is pyloric stenosis diagnosed?

Your baby’s healthcare provider will ask you about your baby’s eating habits and perform a physical exam. Sometimes, providers can feel an olive-sized lump in your baby’s belly (abdomen). That’s the thickened pyloric muscle.

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

What tests will be done to diagnose pyloric stenosis?

If your baby’s healthcare provider doesn’t feel a lump in their belly or wants to confirm the diagnosis, they may want to look for the pyloric stenosis on ultrasound. During an abdominal ultrasound:

  1. Your baby’s provider places a probe (tool) gently against their belly.
  2. The probe uses sound waves to create images.
  3. Their 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 baby’s provider may recommend an upper gastrointestinal (GI) series:

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

Management and Treatment

How is pyloric stenosis treated?

Pyloric stenosis treatment involves a type of pyloroplasty surgery called pyloromyotomy. After diagnosing pyloric stenosis, your baby’s surgeon will discuss the surgery with you.

What happens before pyloric stenosis surgery?

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

Your baby 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, your baby’s healthcare team will:

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

How long does pyloric stenosis surgery take?

The procedure usually takes less than an hour.

Can my baby eat after pyloric stenosis surgery?

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

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

What if my baby 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.
  • A lack of adequate burping after feedings.
  • Too much food, too quickly.

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


Can pyloric stenosis be prevented?

There’s no way to prevent pyloric stenosis. If you know pyloric stenosis runs in your family, make sure to tell your baby’s healthcare provider. Their 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 can I expect if my baby has pyloric stenosis?

The outlook for babies with HPS is very good. Most children don’t 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.

Can pyloric stenosis cause problems later in life?

With treatment, infants experience no long-term issues later in life. In follow-up studies, people who had pyloromyotomy surgery as babies had no trouble with gastroesophageal reflux or other gastrointestinal symptoms as adults.

Living With

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

When you go home from the hospital:

  • Your baby will be eating normally, so you can feed them without problems.
  • Use medication such as acetaminophen (Tylenol®) if your baby experiences any pain.
  • Give your baby a sponge bath the day after surgery. At three days post-surgery, you can bathe them in the tub.
  • A small tape called a Steri-Strip™ will cover the incision. Don’t pull it off yourself — it’ll fall off on its own. If it doesn’t, your baby’s 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 their provider seven to 10 days after surgery. Their provider will examine the surgical area and see how your baby is recovering.

Are there activity restrictions after pyloric stenosis surgery?

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

When should my baby see their healthcare provider?

Some normal swelling around the incision site is normal. But call your baby’s provider if they have:

What questions should I ask my baby’s healthcare provider?

If your baby has signs of pyloric stenosis, you may have several questions for their provider, including:

  • How do I know if my baby is just spitting up or has pyloric stenosis?
  • Is pyloric stenosis a painful condition?
  • Does my baby need surgery?
  • Are there any other treatment options?
  • Will my baby need another surgery?

A note from Cleveland Clinic

A little spit-up is normal for babies. But if your infant is forcefully vomiting after many or all of their feedings, they may have pyloric stenosis. As soon as you notice signs of this condition, contact your baby’s healthcare provider. The sooner they receive a diagnosis and treatment, the better. Delayed treatment can lead to dehydration and undernourishment. The good news is, pyloric stenosis is treatable with surgery, and hopefully, your baby will be healthy and thriving soon.

Medically Reviewed

Last reviewed by a Cleveland Clinic medical professional on 05/11/2023.

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