Final Answer:
The first sign of pyloric stenosis in a baby is mild vomiting that progresses to projectile vomiting. Later, you may be able to palpate a mass, the baby will seem hungry often, and may spit up after feedings.
Step-by-step explanation:
1. *Pyloric Stenosis:* This is a condition characterized by the narrowing of the pylorus, the opening from the stomach into the small intestine, leading to various symptoms.
2. *Mild Vomiting:* The initial symptom is mild vomiting. This represents the early stage of pyloric stenosis.
3. *Progresses to Projectile Vomiting:* As the condition advances, the vomiting becomes more forceful and projectile. This is a distinctive characteristic of pyloric stenosis.
4. *Palpate a Mass:* In later stages, a healthcare provider may be able to feel or palpate a mass in the baby's abdomen. This mass is often the hypertrophied pylorus.
5. *Baby Seeming Hungry Often:* Despite vomiting, the baby may appear hungry frequently. This is because the milk or formula is unable to pass through the narrowed pyloric opening efficiently.
6. *Spitting Up After Feedings:* In addition to projectile vomiting, the baby may experience spitting up after feedings due to the obstruction caused by pyloric stenosis.