lecithin-sphingomyelin ratio
Pronunciation: LES-ih-thin-SFING-go-my-eh-lin
A test of amniotic fluid that assesses fetal lung maturity by measuring surfactant components. Abbreviated as L/S ratio.
Full Definition
A laboratory test performed on amniotic fluid to evaluate fetal pulmonary maturity by measuring the ratio of lecithin to sphingomyelin, two phospholipids found in pulmonary surfactant. The lecithin-sphingomyelin ratio (L/S ratio) increases as the fetal lungs mature, with a ratio of 2:1 or greater generally indicating mature lungs and reduced risk of respiratory distress syndrome in the newborn. This test was historically important for timing elective deliveries before 39 weeks gestation, though it has largely been replaced by phosphatidylglycerol testing and lamellar body counts. The test requires amniocentesis to obtain amniotic fluid and is most accurate after 32 weeks gestation.
Usage
Usage note: L/S ratio is acceptable abbreviation after first use. Always express as a ratio (e.g., 2.1:1) rather than decimal format.
In Context
- "The L/S ratio of 2.5:1 indicated fetal lung maturity at 36 weeks gestation." — Laboratory report
- "Amniocentesis for lecithin-sphingomyelin ratio was performed prior to scheduled cesarean delivery." — Procedure note