Fetal corticosteroid treatment can improve lung function even if surfactant is not increased due to changes in lung structure by increasing what?

• A. Decreased fetal inflammatory response
• B. Increased lung surface area available for gas exchange
• C. Decreased preterm delivery
• D. Increased alveolar edema

Answer: (B)

The key idea is that gas exchange depends on the area available for diffusion. Antenatal corticosteroids promote lung maturation not only by boosting surfactant production but also by accelerating structural development—specifically, alveolarization and the growth of the capillary network. This increases the surface area of the alveolar–capillary interface. Even if surfactant isn’t raised, a larger surface area provides more space for oxygen to diffuse into the blood and for carbon dioxide to exit, improving overall lung function after birth.

Putting it simply, more alveolar surface area means greater diffusing capacity, which helps with gas exchange despite unchanged surfactant levels. The other options don’t address this structural enhancement of the gas-exchange interface: reducing fetal inflammation helps injury prevention but not surface area; shortening time to delivery helps with management but not the diffusion surface; and increasing alveolar edema would impair gas exchange rather than improve it.