Normal L/S ratio?

Normal L/S ratio?

• A. 2:1 or higher. Larger number first
• B. 1:1
• C. 3:4
• D. 4:2

Answer: (A)

The L/S ratio in amniotic fluid gauges fetal lung maturity by comparing lecithin to sphingomyelin. Lecithin rises as the lungs mature, while sphingomyelin stays relatively constant, so the ratio increases with maturity. A ratio of 2:1 or higher means there is enough lecithin to indicate mature surfactant production, reducing the risk of respiratory distress after birth. That’s why 2:1 or greater is considered normal. Ratios like 1:1 or 3:4 reflect insufficient lecithin relative to sphingomyelin and suggest immature lungs. A 4:2 ratio is effectively the same as 2:1, but the standard way to express normal maturity is 2:1 or higher.

The L/S ratio in amniotic fluid gauges fetal lung maturity by comparing lecithin to sphingomyelin. Lecithin rises as the lungs mature, while sphingomyelin stays relatively constant, so the ratio increases with maturity. A ratio of 2:1 or higher means there is enough lecithin to indicate mature surfactant production, reducing the risk of respiratory distress after birth. That’s why 2:1 or greater is considered normal. Ratios like 1:1 or 3:4 reflect insufficient lecithin relative to sphingomyelin and suggest immature lungs. A 4:2 ratio is effectively the same as 2:1, but the standard way to express normal maturity is 2:1 or higher.