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lecithin/sphingomyelin ratio(L-S ratio)
the ratio of lecithin to sphingomyelin in amniotic fluid, the determination of which is helpful in establishing the maturity of the fetus and its susceptibility to hyaline membrane disease after birth.
lec·i·thin/sphin·go·my·e·lin ra·ti·o (L:S ra·ti·o),
a ratio used to determine fetal pulmonary maturity, found by testing the amniotic fluid; when the lungs are mature, lecithin exceeds sphingomyelin by 2 to 1.