Transient tachypnea of the newborn is typically due to which mechanism?

• A. Delayed removal of fetal lung fluid
• B. Pneumothorax
• C. Low birth weight
• D. Hyperglycemia

Answer: (A)

The main concept being tested is that transient tachypnea of the newborn results from delayed clearance of fetal lung fluid after birth. When a baby begins breathing, the lungs switch from a fluid-filled to an air-filled state, and fluid is normally cleared rapidly by active sodium transport in the alveolar epithelium, driven by catecholamines released during labor. If this clearance is delayed, fluid remains in the alveoli and interstitium, increasing airway resistance and impairing gas exchange, which manifests as tachypnea and mild respiratory distress in the hours after birth. This condition is typically self-limited over 24 to 72 hours and is managed with supportive care such as nasal continuous positive airway pressure if needed. Pneumothorax would present with sudden distress and findings of air in the pleural space, not fluid retention. Low birth weight is a risk factor but does not explain the mechanism, and hyperglycemia is not involved in TTN.