How long does betamethasone take to be effective?

• A. 6 hours
• B. 12 hours
• C. 24 hours
• D. 48 hours

Answer: (C)

Betamethasone speeds up fetal lung maturation by increasing surfactant production in the fetus. After the dose is given to the mother, the fetus can start showing the benefits within about 24 hours, with the most noticeable improvement developing over the next day or so. This makes roughly a one-day timeline the best single answer. Six or twelve hours are typically too soon to see meaningful surfactant changes, and waiting until 48 hours would miss the point that the onset begins around 24 hours.