RELATED STORIES • Diaper rash • Urinary tract infections in children: Are bubble baths a culprit? • Infant acid reflux • Thermometers: Taking your child's temperature • Slide show: Choosing a thermometer • Injections: How to make them easier for your child • Slide show: Common baby rashes • Slide show: Holding your child during medical procedures • Infant constipation: How do you treat it? • Babies and the common cold • Colic • What to do when your baby is sick FAMILY HEALTH Parenting Infants • Colic • Diaper rash • Infant jaundice • Spina bifida • Ventricular septal defect (VSD) • Tetralogy of Fallot • Coarctation of the aorta • Umbilical hernia • Ambiguous genitalia • Cleft lip and cleft palate • Infant acid reflux • Pyloric stenosis • Undescended testicle (cryptorchidism) CHILDREN'S HEALTH Illnesses • Colic • Diaper rash • Infant acid reflux • Pyloric stenosis

Note: All links within content go to MayoClinic.com

If you're like most parents, you keep a supply of burp cloths within an arm's reach of your baby. After all, spit up happens — and it's usually nothing to worry about. Sometimes, however, forceful spitting up is a sign of a more serious condition known as pyloric stenosis.

Pyloric stenosis is an uncommon condition that affects the pylorus, the opening at the lower end of the stomach that connects the stomach and small intestine. In babies with pyloric stenosis, the muscles of the pylorus become abnormally large. This prevents food from entering the small intestine. Pyloric stenosis can lead to forceful vomiting, dehydration, weight loss and electrolyte imbalances. Prompt surgical treatment is important.

Pyloric stenosis affects an estimated two to four of every 1,000 infants. It's typically diagnosed three to 12 weeks after birth. Pyloric stenosis is rare in children older than 6 months.

At first, a baby who has pyloric stenosis may not look sick or appear uncomfortable. Watch for these signs:

• Projectile vomiting. Pyloric stenosis often causes projectile vomiting — the forceful ejection of milk or formula up to several feet away — within 30 minutes of feeding. Vomiting may be mild at first and gradually become more severe. Rarely, the vomit may contain blood.
• Persistent hunger. Babies with pyloric stenosis often want to eat soon after vomiting.
• Stomach contractions. You may notice wave-like contractions that move across your baby's upper abdomen (peristalsis) soon after feeding but before vomiting. This is caused by stomach muscles trying to force food past the outlet of the pylorus.
• Dehydration. Your baby may cry without tears or become lethargic. You may find yourself changing fewer wet diapers or diapers that aren't as wet as you expect.
• Changes in bowel movements. Since pyloric stenosis prevents food from reaching the intestines, babies with this condition often have smaller and fewer stools. Bowel movements may be loose and green and contain mucus.
• Weight problems. Pyloric stenosis can prevent a baby from gaining weight. Sometimes pyloric stenosis leads to weight loss.

The causes of pyloric stenosis are unknown, but genetic factors may play a role.

Pyloric stenosis is more common in whites than blacks, Hispanics or Asians. It affects more males than females — particularly firstborn males.

Contact your baby's doctor if you suspect pyloric stenosis. Watch for:

• Frequent vomiting after feeding
• Projectile vomiting
• Decreased activity
• Infrequent wet or dirty diapers — up to six hours between wet diapers or a day or two without a bowel movement
• Failure to gain weight or weight loss

Signs and symptoms of pyloric stenosis can mimic those of other conditions that cause infant vomiting, including gastroesophageal reflux disease (GERD). Your baby's doctor may use various strategies to make the diagnosis:

• Medical history. Be prepared to answer questions about your baby's vomiting. Describe any patterns in when the vomiting occurs and what the vomit looks like. This may not be pleasant, but the details are important.
• Physical exam. Your baby's doctor may feel an olive-shaped lump — the enlarged pyloric muscle — when examining your baby's abdomen.
• Blood tests. The loss of electrolytes — such as sodium, potassium, magnesium and calcium — may be a sign of continual vomiting and dehydration.
• Ultrasound. This test uses sound waves to create an image of your baby's stomach.
• Contrast X-ray. For this test, your baby swallows a small amount of a liquid that coats the stomach. This contrast material helps any abnormalities show up more clearly on an X-ray.

Pyloric stenosis can lead to dehydration, the loss of electrolytes and weight problems. Repeated vomiting can irritate your baby's stomach. A few infants with pyloric stenosis develop jaundice — a yellowish discoloration of the skin and eyes.

Pyloric stenosis is typically treated with a surgical procedure known as pyloromyotomy. During the procedure, which is done under general anesthesia, the surgeon cuts and spreads apart the outside layer of the thickened pyloric muscles. The inside lining of the pylorus is left intact.

Before surgery, your baby may be given intravenous (IV) fluids to treat dehydration and restore electrolytes. Your baby may receive IV fluids for a few hours after surgery as well, until he or she can tolerate normal feedings.

Signs and symptoms of pyloric stenosis usually stop within about 24 hours after surgery. Most infants return home within 48 hours. Your baby's doctor may request a follow-up visit after surgery to check on your baby's recovery.