<<Disclaimer: Verify this information before applying it to your situation.>> This some of the information that I have on Lecithin; don't know if it's what you are looking for: Lecithin: Sphingomyelin ratio. The ratio of lecithin to the sphingomyelin in the amniotic fluid. It is used to assess maturity of the fetal lung. Until about the 34th week of gestation the lungs produce less lecithin than sphingomyelin. As the fetal lungs begin to mature, they produce more lecithin than sphingomyelin. Delivery before the reversal of the ratio is associated with an increased risk of hyaline membrane disease in the infant. The use of this test enables the obstetrician to determine the optimum time for elective termination of pregnancy. Clelia