Pharyngeal lecithin/sphingomyelin ratios in newborn infants.

Lecithin/sphingomyelin ratios were measured on hypopharyngeal secretions from newborn infants within 6 h of birth. L/S ratios of 1.8 or less correlated with the development of the idiopathic respiratory-distress syndrome. Low L/S ratios were more common in the shorter gestation infants, and there was a predominance of L/S ratios of more than 1.8 above 32 weeks' gestation. In multiple births, the first-born of triplets and quadruplets had higher L/S ratios than those subsequently born. This may indicate a link between fetal lung maturation and the onset of labour.