Antenatal corticosteroids are administered to a woman with threatened preterm delivery at 30 weeks gestation. By what primary mechanism do they reduce the severity of neonatal respiratory distress syndrome?
- A Direct relaxation of pulmonary vascular smooth muscle
- B Induction of surfactant protein and phospholipid synthesis by type II pneumocytes ✓
- C Acceleration of alveolar septation and increase in alveolar number
- D Suppression of maternal antibodies crossing the placenta
Correct answer: B. Induction of surfactant protein and phospholipid synthesis by type II pneumocytes
Explanation
Glucocorticoids act on type II pneumocytes to induce enzymes of phospholipid synthesis and the surfactant proteins SP-A, SP-B and SP-C, increasing surfactant stores before birth and reducing alveolar collapse. They also accelerate structural lung maturation but the clinically decisive effect is biochemical induction of surfactant. Maximal benefit is seen if delivery occurs 24 hours to 7 days after the first dose, between 24 and 34 weeks of gestation.
Reference: Williams Obstetrics, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.