Secondary pulmonary hypoplasia is most commonly caused by which of the following?

• A. Congenital diaphragmatic hernia (CDH)
• B. Intrauterine growth restriction (IUGR)
• C. Persistent pulmonary hypertension (PPHN)
• D. Neonatal sepsis

Answer: (A)

Secondary pulmonary hypoplasia arises when fetal lung growth is limited by factors outside the lung tissue itself. The most common culprit is congenital diaphragmatic hernia, in which abdominal organs herniate into the chest and crowd the developing lungs. This space constraint dramatically reduces lung growth, leading to smaller airways, fewer alveoli, and an underdeveloped pulmonary vasculature. The result is a neonate with severe respiratory distress and a higher risk of pulmonary hypertension after birth. Other conditions like intrauterine growth restriction can produce smaller lungs but do not cause the same direct, characteristic hypoplasia as CDH. Persistent pulmonary hypertension is usually a consequence of underdeveloped lungs, not the initial cause, and neonatal sepsis does not initiate pulmonary hypoplasia.