Babies with pyloric stenosis typically vomit after most or all feedings, though some vomit after only some feedings, especially early on. The vomiting is forceful and projectile, not the gentle dribble of normal spit-up, and it usually happens within 30 minutes to an hour after eating. As the condition worsens over days, the vomiting becomes more frequent and more forceful.
What the Vomiting Looks Like
The hallmark of pyloric stenosis is projectile vomiting, meaning the stomach contents are expelled with enough force to travel several feet. This is distinctly different from the passive spit-up that most newborns do. Normal spit-up dribbles out of the mouth, often during or right after a burp. Projectile vomiting looks alarming: the milk comes out fast and hard, sometimes landing well away from the baby.
The vomit is usually undigested breast milk or formula. It doesn’t contain bile (the greenish-yellow digestive fluid), because the blockage sits above the point where bile enters the digestive tract. If your baby is vomiting green or yellow fluid, that points to a different problem entirely.
How Often and When It Happens
There’s no single number of episodes per day that defines pyloric stenosis. Some babies vomit after every single feeding. Others vomit after most feedings but keep some down. In the early days of the condition, a baby might only vomit occasionally, making it easy to mistake for normal newborn fussiness or reflux. Over the course of a week or two, though, the pattern becomes harder to miss: the vomiting gets more frequent, more forceful, and more consistent.
The timing is predictable. Vomiting episodes cluster within 30 minutes to one hour after a feeding. Between episodes, the baby often acts hungry and eager to eat again, which catches many parents off guard. A baby who just threw up an entire feeding and immediately wants more is a classic sign of pyloric stenosis. The baby’s stomach is trying to push food through a passage that’s too narrow, so the food comes back up, but the hunger signals remain.
When Symptoms First Appear
Symptoms typically show up between 3 and 6 weeks of age. About 95% of cases are diagnosed between 3 and 12 weeks. It’s rare for pyloric stenosis to appear in babies older than 3 months. The condition develops gradually as the muscle surrounding the stomach’s outlet thickens, so vomiting often starts mild and escalates. Parents frequently describe a progression: occasional forceful vomiting in the first few days, followed by vomiting after nearly every feeding within a week or so.
Signs the Vomiting Is Becoming a Problem
Because the baby can’t keep enough milk down, dehydration and weight loss follow quickly. A dehydrated infant may have dry skin and a dry mouth, produce fewer tears when crying, and have noticeably fewer wet diapers. The soft spot on top of the head (the fontanelle) can appear sunken. The baby may seem increasingly lethargic or irritable between feedings.
Weight is another clear signal. A healthy newborn should be gaining weight steadily. A baby with pyloric stenosis will plateau or lose weight because so little nutrition makes it through. If your baby seems constantly hungry, is vomiting forcefully after feedings, and isn’t gaining weight, those three signs together strongly suggest pyloric stenosis.
How It’s Diagnosed
Doctors can sometimes feel the thickened pyloric muscle during a physical exam. It’s often described as a small, firm lump (about the size of an olive) in the upper right area of the baby’s abdomen. This finding is present in 60 to 80% of infants with the condition. When it can’t be felt, an ultrasound confirms the diagnosis quickly and painlessly. Early in the course of the disease, the classic signs may not all be present yet, which is why some babies need a follow-up visit or imaging to get a definitive answer.
What Happens After Surgery
Pyloric stenosis is treated with a surgical procedure that cuts through the thickened muscle to open the passage from the stomach into the intestine. Recovery is fast. Most babies start small feedings within hours of waking from anesthesia and work back up to a normal feeding schedule within 24 to 48 hours. A typical hospital stay is one to two days.
Some vomiting can continue for a short period after surgery while the stomach fully heals. This is normal and much milder than the pre-surgery vomiting. Parents are usually told to watch for a steady improvement in feeding tolerance over the first few days at home. Once healed, the condition does not come back, and babies go on to eat and grow normally.