Pyloric Stenosis in Babies
Content reviewed against published AAP, NIH, Mayo Clinic guidelines
Last reviewed:
Pyloric stenosis is a condition in which the muscle (pylorus) at the outlet of the stomach thickens and swells, blocking food from passing into the small intestine. It causes progressively worsening projectile vomiting in infants, typically presenting between 2-8 weeks of age. It is the most common surgical cause of vomiting in infancy and requires surgical correction.
Key takeaways
- Pyloric stenosis is a condition in which the muscle (pylorus) at the outlet of the stomach thickens and swells, blocking food from passing into the small intestine.
- Duration: Pre-operative: symptoms develop over 1-3 weeks and do not resolve without surgery. Post-operative: most infants recover fully within 24-48 hours after surgery and are discharged within 1-2 days. Full feeding is typically established within 1 week of surgery.
- Go to ER if: Projectile vomiting with signs of dehydration (no tears, dry mouth, sunken fontanelle)
- No vaccine currently available
Symptoms
How It Presents by Age
0-2 weeks
Uncommon but can present this early, especially if mother took erythromycin late in pregnancy or baby received it early. May be difficult to distinguish from normal spit-up initially.
Risk level: Moderate
2-5 weeks
Classic presentation age. Vomiting starts mild and progressively becomes forceful/projectile over days to weeks. Baby is hungry immediately after vomiting. Non-bilious (never green). Weight plateau or loss develops.
Risk level: High — peak onset period
5-12 weeks
Later presentation. Vomiting is clearly projectile by this point. Baby may be significantly dehydrated and underweight. More obvious on examination. Electrolyte abnormalities more likely (hypochloremic metabolic alkalosis).
Risk level: High if dehydrated
3-6 months
Rare but documented. Late presentation may be more subtle. Important to consider in any infant with non-bilious projectile vomiting.
Risk level: Moderate
Treatment
Pyloromyotomy (surgery)
The definitive treatment. Ramstedt pyloromyotomy involves cutting through the thickened pyloric muscle while leaving the inner lining intact, allowing food to pass. Most commonly performed laparoscopically. Cure rate is essentially 100%.
Pre-operative fluid resuscitation
Before surgery, IV fluids with appropriate electrolyte correction (especially chloride and potassium) to correct metabolic alkalosis. Surgery is delayed until electrolytes are normalized — this is NOT an emergency surgery.
NPO (nothing by mouth)
Baby is kept NPO prior to surgery to reduce vomiting and aspiration risk.
Post-operative feeding
Gradual reintroduction of feeds beginning 4-6 hours after surgery. Small, frequent feedings are advanced as tolerated. Some vomiting in the first 24-48 hours post-op is normal.
Home Care
- There are no home remedies for pyloric stenosis — it requires surgical correction
- If awaiting medical evaluation, keep baby upright after feeds
- Offer smaller, more frequent feedings to reduce vomiting volume
- Track feeding amounts, vomiting episodes, and wet diapers
- Do not delay seeking medical care — dehydration can worsen quickly
- After surgery: feed baby in upright position and burp frequently
- After surgery: offer small frequent feeds as instructed by surgeon
When to Worry
Go to the ER if:
- Projectile vomiting with signs of dehydration (no tears, dry mouth, sunken fontanelle)
- Baby is lethargic or difficult to wake
- No wet diaper for 6+ hours
- Blood in vomit (may look like coffee grounds)
- Green (bilious) vomiting — this is NOT pyloric stenosis and suggests a different surgical emergency
- Post-surgery: wound infection signs, bile-stained vomiting, or inconsolable pain
Call your doctor if:
- Progressively worsening vomiting in an infant 2-8 weeks old
- Projectile vomiting (vomit travels across the room, not just spitting up)
- Baby is always hungry after vomiting
- Fewer wet diapers than normal
- No weight gain or weight loss at a well-check visit
- Post-surgery: fever, redness at incision, or excessive vomiting beyond 48 hours
Keep an eye on:
- Vomiting is becoming more forceful (projectile) over days
- Baby vomits with every feed and is hungry immediately after
- Fewer wet diapers (less than 4 per day)
- Baby is not gaining weight or losing weight
- Visible rippling or waves across the stomach
- Baby is becoming increasingly lethargic
Prevention
- There is no proven way to prevent pyloric stenosis
- Avoid macrolide antibiotics (erythromycin, azithromycin) in infants under 6 weeks unless absolutely necessary
- Breastfeeding may be slightly protective
- Be aware of increased risk in firstborn males and those with family history
- Report any erythromycin use in the first 2 weeks of life to your pediatrician
Contagion & Incubation
Incubation
Not applicable — this is not an infection. Symptoms typically begin at 2-8 weeks of age, with peak onset at 3-5 weeks.
Contagious for
Not contagious.
Duration
Pre-operative: symptoms develop over 1-3 weeks and do not resolve without surgery. Post-operative: most infants recover fully within 24-48 hours after surgery and are discharged within 1-2 days. Full feeding is typically established within 1 week of surgery.
Frequently asked questions
How long does pyloric stenosis last?
How does infantile hypertrophic pyloric stenosis (ihps) spread?
When should I take my baby to the ER?
Can infantile hypertrophic pyloric stenosis (ihps) be prevented?
When can my child return to daycare?
Sources
All content follows our editorial policy and is reviewed against published clinical guidelines.
2,705 evidence-based guides6 authoritative medical sources
Related Illnesses
Bottom line
Pyloric Stenosis is treatable with appropriate medical care. Seek emergency care if projectile vomiting with signs of dehydration (no tears, dry mouth, sunken fontanelle).
Trust your instincts. If something feels wrong, reach out to your pediatrician. Worrying about your baby means you care — that is a good thing.