## **Core Concept**
Surfactant deficiency is a critical condition that affects the lungs, particularly in newborns. **Surfactant** is a complex mixture of phospholipids and proteins that reduces surface tension in the alveoli, facilitating easier lung expansion during breathing. Its deficiency leads to increased surface tension, making lung expansion more difficult.

## **Why the Correct Answer is Right**
The correct answer, **Premature infants**, experience surfactant deficiency due to the immaturity of their lungs. Surfactant production begins around the 24th to 28th week of gestation, and its levels increase significantly thereafter. Premature infants, especially those born before 28 weeks, often have underdeveloped type II pneumocytes, which are responsible for surfactant production. This deficiency leads to **neonatal respiratory distress syndrome (NRDS)**, characterized by difficulty breathing, increased work of breathing, and often, the need for mechanical ventilation and surfactant replacement therapy.

## **Why Each Wrong Option is Incorrect**
- **Option A: Full-term infants** - These infants typically have mature lungs with sufficient surfactant production, making surfactant deficiency less common.
- **Option B: Children with cystic fibrosis** - While cystic fibrosis affects the lungs and leads to respiratory complications, it is not primarily associated with surfactant deficiency. The disease causes thick, sticky mucus to build up in the lungs, leading to infections and lung damage.
- **Option C: Adults with pneumonia** - Adults with pneumonia may have inflammation and fluid buildup in the lungs, but this condition is not directly caused by surfactant deficiency, although surfactant function can be indirectly affected.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that **antenatal corticosteroid administration** to mothers at risk of preterm delivery is a strategy to accelerate fetal surfactant production, reducing the incidence and severity of NRDS in premature infants. This is a critical preventive measure in neonatal care.

## **Correct Answer: B. Premature infants**