title: Letter: Lecithin/sphingomyelin ratio in tracheal aspirate.
mesh_terms: D001722:Birth Order; D005122:Exudates and Transudates / Q000032:analysis*; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D008168:Lung / Q000196:embryology*; D010713:Phosphatidylcholines / Q000032:analysis*; D011247:Pregnancy; D011783:Quadruplets; D013109:Sphingomyelins / Q000032:analysis*; D014132:Trachea / Q000378:metabolism; D014310:Triplets
chemical_list: D010713:Phosphatidylcholines; D013109:Sphingomyelins