By what week does the fetus typically start producing surfactant in the lungs?

The production of surfactant in the lungs typically begins around week 24 of gestation. Surfactant is crucial for reducing surface tension in the alveoli, thereby preventing their collapse and facilitating normal breathing after birth.

Between weeks 24 and 28, there is a significant increase in the amount of surfactant produced, with levels reaching a point that enhances the fetus's chances of survival outside the womb if born prematurely. The lung development process is key to preparing the fetus for breathing air, and by around week 28, the production of surfactant becomes even more pronounced.

The fact that surfactant production begins around week 24 underscores the importance of this timeframe in fetal development, as it marks a critical step toward the maturation of the respiratory system. Therefore, the option indicating week 20 does not align with known fetal lung development stages, as surfactant production starts later.