The L/S ratio is used to assess what aspect of fetal physiology?

The L/S ratio is used to assess what aspect of fetal physiology?

• A. Liver maturity
• B. Fetal lung maturity
• C. Renal development
• D. Placental function

Answer: (B)

The L/S ratio measures fetal lung maturity by evaluating surfactant content in amniotic fluid. Surfactant, particularly lecithin (phosphatidylcholine), increases as the fetal lungs mature, while sphingomyelin stays relatively constant early on. As the ratio rises, it indicates more mature lungs and a lower risk of neonatal respiratory distress syndrome after birth. Clinically, a ratio above about 2:1 is considered evidence of lung maturity, with some settings using 2.5:1 as a more conservative threshold. The test is done on amniotic fluid obtained by amniocentesis because surfactant appears in the fluid as the lungs mature. This helps guide timing of delivery in pregnancies at risk for preterm birth.

The L/S ratio measures fetal lung maturity by evaluating surfactant content in amniotic fluid. Surfactant, particularly lecithin (phosphatidylcholine), increases as the fetal lungs mature, while sphingomyelin stays relatively constant early on. As the ratio rises, it indicates more mature lungs and a lower risk of neonatal respiratory distress syndrome after birth. Clinically, a ratio above about 2:1 is considered evidence of lung maturity, with some settings using 2.5:1 as a more conservative threshold. The test is done on amniotic fluid obtained by amniocentesis because surfactant appears in the fluid as the lungs mature. This helps guide timing of delivery in pregnancies at risk for preterm birth.