Which mechanism contributes to fetal lung structural maturation in response to antenatal steroids?

• A. Decrease in alveolar capillary density
• B. Increase in gas exchange surface area
• C. Reduction in alveolar type II cells
• D. Decrease in lung volume

Answer: (B)

Antenatal steroids accelerate fetal lung structural maturation by boosting the growth of the gas-exchange interface—the alveolar-capillary surface area. They stimulate type II pneumocyte maturation and surfactant production, promote alveolar septation, and support capillary development, all of which expand the number and size of alveoli with a larger surface area for diffusion. This increased gas-exchange surface area is what enhances lung readiness after birth. Decreases in alveolar capillary density, reductions in type II cells, or decreases in lung volume would hinder maturation, not promote it.