Lecithin–sphingomyelin ratio

Lecithin–sphingomyelin ratio
Sphingomyelin

The lecithin–sphingomyelin ratio (L/S ratio or L-S ratio) is a test of

The lecithin–sphingomyelin ratio is a marker of fetal lung maturity. The outward flow of pulmonary secretions from the fetal lungs into the amniotic fluid maintains the level of lecithin and sphingomyelin equally until 32–33 weeks gestation, when the lecithin concentration begins to increase significantly while sphingomyelin remains nearly the same. As such, if a sample of amniotic fluid has a higher ratio, it indicates that there is more surfactant in the lungs and the baby will have less difficulty breathing at birth. An L–S ratio of 2.4 or more indicates fetal lung maturity and a relatively low risk of infant respiratory distress syndrome, and an L/S ratio of less than 1.5 is associated with a high risk of infant respiratory distress syndrome.

If

• Phosphatidylglycerol – another amniotic fluid marker of fetal lung maturity
• Surfactant-albumin ratio
• Lamellar body count

References