The Lecithin : sphingomyelin ratio is measured for assessing maturity of:

The Lecithin : sphingomyelin ratio is measured for assessing maturity of the fetal lung. This test depends on outward flow of pulmonary secretions from the lungs into the amniotic fluid. At about 35 weeks of gestation this ratio reaches a value of 2. Commonly used direct tests of fetal lung maturity: Lecithin/sphingomyelin ratio Phosphatidylglycerol Fluorescence polarization Foam-stability index Optical density at 650 nm Lamellar body counts Ref: Mehta S.H., Sokol R.J. (2013). Chapter 12. Assessment of At-Risk Pregnancy. In A.H. DeCherney, L. Nathan, N. Laufer, A.S. Roman (Eds),CURRENT Diagnosis & Treatment: Obstetrics & Gynecology, 11e.