title: Letter: Lecithin/sphingomyelin ratios and sex incidence of respiratory-distress syndrome.
mesh_terms: D000653:Amniotic Fluid / Q000032:analysis*; D005260:Female; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D008168:Lung / Q000196:embryology; D008297:Male; D010713:Phosphatidylcholines / Q000032:analysis*; D011247:Pregnancy; D012127:Respiratory Distress Syndrome, Newborn / Q000453:epidemiology* / Q000209:etiology; D012737:Sex Factors; D012744:Sex Ratio; D013109:Sphingomyelins / Q000032:analysis*
chemical_list: D010713:Phosphatidylcholines; D013109:Sphingomyelins