What does a Lecithin/Sphingomyelin (L/S) ratio of less than 2 typically suggest?

A Lecithin/Sphingomyelin (L/S) ratio of less than 2 is indicative of immature lungs. In the context of fetal development, this ratio is used to assess lung maturity, particularly in at-risk pregnancies. Lecithin is a phospholipid component of surfactant, which is produced by type II alveolar cells in the lungs. As the fetus approaches term, the production of lecithin increases relative to sphingomyelin, leading to a higher L/S ratio.

When the ratio is less than 2, it suggests that there is insufficient production of surfactant, which is essential for keeping the alveoli open and preventing atelectasis (collapse of the lung). This immature lung condition can be a precursor to respiratory distress syndrome (RDS), a common complication in preterm infants due to inadequate surfactant levels.

In summary, a low L/S ratio is a key indicator of lung immaturity, highlighting the need for monitoring and potential interventions to support respiratory function in the neonate.