What Is Pyloric Stenosis?

Medically Reviewed by Renee A. Alli, MD on July 03, 2021
4 min read

Pyloric stenosis is a rare condition that makes the valve between a newborn's stomach and small intestine get thick and narrow. This makes it harder for food to go from the baby's stomach into the intestine.

It affects about three out of every 1,000 babies born in the United States.

Signs of pyloric stenosis usually show up when a baby is 3 to 5 weeks old. Babies who have it don't look sick, but they throw up a lot. Sometimes they projectile vomit -- this means it can go several feet into the air. It also might smell sour because it comes from your baby's stomach, where it’s been mixed with stomach acid.

In time, your baby might vomit more and more often. Some babies with this condition can't keep any food down.

It doesn't affect babies’ appetites, though -- they’re often hungry again soon after they throw up.

Other symptoms include:

  • Signs of dehydration (your baby’s body doesn’t have enough water): fewer wet diapers than usual, few to no tears, a sunken soft spot on the head, and sunken eyes
  • Fewer soiled diapers than usual
  • Weight loss or no weight gain
  • Ripples across the baby's stomach -- a sign the stomach muscles are working hard to move food into the intestines
  • Lump in the abdomen
  • More fussiness

Call your pediatrician if your baby has symptoms like these -- pyloric stenosis needs to be treated right away.

The pylorus is a valve that sits between the stomach and small intestine. It stays closed to hold food in the stomach, then it opens to let food move into the intestine, where it’s digested.

In babies with pyloric stenosis, the pylorus gets thicker, and food moves into the small intestine more slowly. When food can't get from the stomach into the intestine, the baby throws it back up.

Doctors don't know exactly why the pylorus gets bigger, but it might be partly caused by changes in a gene. It's often passed down through families. If one or both parents have pyloric stenosis, their baby has up to a 20% greater chance of getting it.

Other things that can make a baby more likely to have it include:

  • Gender: Boys are more likely to get pyloric stenosis than girls.
  • Premature birth: Babies born before the 37th week of pregnancy have a higher chance of having it.
  • Smoking during pregnancy: Babies of moms who smoke are more than twice as likely to get pyloric stenosis.
  • Certain antibiotics: A baby’s chances may be higher if the mom took erythromycin or azithromycin at the end of their pregnancy, or while breastfeeding, or the baby took them in the first few weeks of life.


Your pediatrician will ask questions about your baby's symptoms. Tell the doctor how often they throw up and what the vomit looks like. The doctor will also check your child's weight and growth. Then they’ll feel your baby's belly for any lumps: An enlarged pylorus feels like an olive.

Your baby’s doctor may want to get a closer look with one of these:

  • Ultrasound: This uses sound waves to make images of the inside of your baby’s stomach.
  • Barium swallow with upper GI series: Your baby drinks a special liquid that has the chemical element barium in it, then special X-rays are taken of the stomach. Barium makes the stomach and intestine show up more clearly.

Your baby also might need blood tests to check levels of things like sodium and potassium. If your baby throws up often, they can lose too much of these important minerals.

Your baby will first get fluids and nutrients through an IV to treat dehydration -- they’ll drip in through a needle that goes directly into a vein. Then surgery (called pyloromyotomy) will be done to open up the blockage.

Your baby will get medicine to make them sleep, so the surgery won’t hurt. The surgeon cuts open the thickened pylorus muscle to create a wider passage for food to travel into the intestine. Sometimes, this can be done with tiny instruments through very small cuts in the baby's belly. This is called laparoscopy.

The surgery takes between 15 minutes and an hour.

Your baby should be able to go home a day or two later. Babies usually go back to eating normally right away, but some may vomit for a few days afterward.