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Hypertrophic Pyloric Stenosis (HPS) - Help for Babies with Forceful Vomiting

Help for Babies with Forceful Vomiting - HPS Help for Babies with Forceful Vomiting - HPS

After a baby's feeding, many new parents quickly learn, some of what goes down often comes back up. While occasional dribbles of spit-up after meals is common in infants and usually harmless, true vomiting is more concerning.

In some babies, frequent projectile vomiting can be a symptom of a condition called hypertrophic pyloric stenosis (HPS); it occurs in 1 out of every 500 or so babies.

What is hypertrophic pyloric stenosis (HPS)?

Pyloric stenosis is a narrowing of the pylorus―a muscular valve at the bottom of the stomach. When it becomes too thick (hypertrophied), breastmilk or formula can't get through to the small intestines. This leads to excessive, projectile vomiting.

Symptoms of pyloric stenosis

Infants with pyloric stenosis have a hard time keeping anything down after feedings―usually starting between 2 and 8 weeks of age.

Signs your baby may have hypertrophic pyloric stenosis

  • Vomiting after every feeding or only after some feedings. Because breastmilk or formula is blocked from passing through the stomach, the baby throws up—sometimes forcefully enough to launch their stomach contents several feet away! The vomiting may gradually get worse as the pylorus muscle thickens.

  • Hungry all the time. Babies with pyloric stenosis may be hungry still (or again) after vomiting. It may seem like they are always hungry.

  • Tummy tightening. After feedings, you may notice waves of contractions ripple across the top of your baby's abdomen, from left to right, as the stomach tries to push food through the pylorus.

  • Constipation. Because pyloric stenosis prevents what babies eat from reaching the intestines, they may become constipated.

  • Dehydration and weight loss. Babies with pyloric stenosis do not get enough fluids and nutrients from feedings and may become dangerously dehydrated. They may have trouble gaining weight as they grow, or even lose weight. See Signs of Dehydrations in Infants & Children for more information.

Be sure to talk with your pediatrician right away if your baby is vomiting a lot.

How is pyloric stenosis diagnosed?

Your doctor may diagnose pyloric stenosis by examining your baby's tummy to feel the thick pylorus muscle―an olive-shaped mass in the upper belly, which is the abnormal pylorus. Imaging tests may be ordered to confirm the diagnosis:

  • Ultrasound can be used to take a picture of the pylorus, which will be thicker and longer than normal. An ultrasound can also show when milk or formula does not pass out of the stomach into the small intestine.

  • Upper gastrointestinal contrast study (or "upper GI"), an X-ray test, is sometimes done. In an upper GI, your baby drinks a liquid that lights up on X-ray. As with ultrasound, if your baby has pyloric stenosis, the upper GI will show only a very small amount of liquid passing through the pylorus.

Are some babies more likely to get diagnosed with pyloric stenosis than others?

The cause of pyloric stenosis is unknown, but researchers point to possible risk factors:

  • Gender. The condition is four times more common in boys than in girls.

  • Race. Caucasian babies are more likely to develop pyloric stenosis than other races.

  • Family history. Sometimes, pyloric stenosis runs in families. Siblings of children with the condition carry a 30 times greater risk than the general population.

  • Early antibiotic use. Babies given certain antibiotics in the first weeks of life—erythromycin to treat whooping cough, for example—have an increased risk of developing pyloric stenosis. Additionally, babies born to mothers who took certain antibiotics late in pregnancy may have an increased risk of developing the condition.

  • Smoking during pregnancy. Babies whose mothers smoked can have nearly double the risk of developing pyloric stenosis.

  • Hernias. Although most infants with pyloric stenosis are otherwise healthy, the condition is seen more often in infants born with inguinal hernias.

  • Bottle-feeding. Some studies suggest that bottle-feeding can raise the risk of pyloric stenosis. But it is not clear whether any rise in risk is related to formula or bottle-feeding itself.

Treatment for pyloric stenosis

Observation. Without treatment, pyloric stenosis will not go away on its own. Once a baby has a hard time keeping anything down, observation alone can result in potentially life-threatening dehydration or malnourishment.

Medicine. Atropine sulfate is the only currently available medication to treat pyloric stenosis. Using this medication requires staying in the hospital for several weeks and giving the baby special IV nutrition until the vomiting goes away. It does not work 10-25% of the time. For these reasons, it is not widely used and recommended only when surgery would be too dangerous for the baby.

Surgery. The only dependable way to fix pyloric stenosis is to open the thickened pylorus muscle with surgery, a procedure called pyloromyotomy. Pyloric stenosis surgery is often done laparoscopically, using a video camera and a few tiny cuts or incisions. Alternatively, it can also be done open with a single longer cut.

What to expect after your baby's pyloromyotomy surgery

After surgery, your baby will be allowed to eat by mouth. Infants should be given breast milk or formula every 3 to 4 hours, starting around 4 to 6 hours after the surgery. Your surgeon will discuss the feeding plan with you after surgery. Know your baby may still have some vomiting, but it usually gets better after a few feedings.

Most babies can go home from the hospital within one day after surgery. However, some may stay longer if they are not eating well. After leaving the hospital, your baby can go back to all normal activities, including tummy time.

Once home, be sure you:

  • Know how to care for your baby's wound. Keep surgical cuts on your baby's tummy clean and dry for 3 days. Afterwards, the wounds may be washed with soap and water but not soaked for about 7 days after surgery. Most of the time, the stitches used in children are absorbable and don't need to be taken out. After 3 days, your baby can go back to usual bath routines.

  • Give medicines as directed―including infant acetaminophen if your baby seems uncomfortable.

  • Make any needed follow-up appointments. Your baby's surgeon and pediatrician will want to make sure your baby is eating well, gaining weight, and recovering fully.

Be sure to call the doctor if:

  • Your baby gets a fever; this could be a sign of a post-op infection. In infants, a fever means a rectal temperature reading of 100.4 degrees Fahrenheit (38 degrees Celsius) or higher, or an oral reading of 99 degrees Fahrenheit (37.2 degrees Celsius) or above.

  • You're concerned about the incision―especially if the cuts on your baby's tummy and the skin around them become red, bleed, or start to have yellow or green discharge (see Staphylococcal Infections).

  • Your baby is vomiting often or after most meals.

  • Your baby's belly appears to be swelling.

  • Your baby is not wetting as many diapers as usual.


Pyloric stenosis is the most frequent surgical condition in infants in the first few months of life. It is important to diagnose pyloric stenosis early, before a baby becomes dehydrated or malnourished. With prompt treatment, babies will soon be able to keep down what they eat so they can grow and thrive.

More information

Last Updated
American Academy of Pediatrics (AAP) Section on Surgery, American Pediatric Surgical Association & American College of Surgeons & AAP Section on Gastroenterology, Hepatology & Nutrition (Copyright © 2022)
The information contained on this Web site should not be used as a substitute for the medical care and advice of your pediatrician. There may be variations in treatment that your pediatrician may recommend based on individual facts and circumstances.
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