**Question:** Most common cause of stridor shortly after birth –

A. Urea cycle disorder
B. Anaphylaxis
C. Foreign body aspiration
D. Subglottic stenosis

**Core Concept:** Stridor is a high-pitched, wheezing sound produced during breathing, indicative of a narrowing or obstruction in the airways, most commonly in the upper respiratory tract. In the context of newborns, this typically refers to the airway structures near the larynx or glottis.

**Why the Correct Answer is Right:** The correct answer, D. Subglottic stenosis, refers to a narrowing or stricture of the subglottic area, located between the larynx and trachea. This narrowing can be congenital or acquired, leading to stridor in infants due to airway obstruction.

**Why Each Wrong Option is Incorrect:**

A. Urea cycle disorder (e.g., ornithine transcarbamylase deficiency) is a rare genetic disorder affecting the urea cycle, which is essential for nitrogen waste elimination. It does not cause stridor but presents with life-threatening hyperammonemia and encephalopathy.

B. Anaphylaxis is a severe, life-threatening allergic reaction affecting multiple organs, characterized by hypotension, shock, and other systemic symptoms. It is not the most common cause of stridor shortly after birth.

C. Foreign body aspiration (e.g., choking on meconium, meatal plug, etc.) results in coughing, choking, and respiratory distress, not stridor. Although foreign body aspiration can cause stridor, it is less common than subglottic stenosis in the given options.

**Clinical Pearl:** Subglottic stenosis is the most common cause of stridor in newborns, resulting from congenital or acquired factors like intubation, caesarean section, or iatrogenic injury during intubation. Early recognition and management of stridor is crucial as it can be life-threatening if left untreated.

**Core Concept:** Subglottic stenosis is a narrowing or stricture of the subglottic area, which can be congenital or acquired. This condition presents as stridor in newborns due to the obstruction of the airway, causing abnormal breathing sounds and potentially life-threatening respiratory distress.

**Why Each Wrong Option is Incorrect:**

A. Urea cycle disorders (e.g., ornithine transcarbamylase deficiency) are rare genetic disorders affecting the urea cycle, causing hyperammonemia and encephalopathy. They do not typically present with stridor.

B. Anaphylaxis is a severe allergic reaction involving multiple organs and systems, typically characterized by hypotension, shock, and systemic symptoms. It is not the most common cause of stridor shortly after birth.

C. Foreign body aspiration, such as choking on meconium or meatal plug, results in coughing, choking, and respiratory distress but is less common than subglottic sten