The lecithin/sphingomyelin ratio in a high-risk obstetric population.

An experience with the lecithin/sphingomyelin (L/S) ratio in a population of high-risk obstetric patients is presented. A wide range of values in ralation to gestational age was found. A delayed rise in L/S ratio was found in Class A diabetes and Rh sensitization but was most striking in Class B through F diabetes. Chronic hypertension alone or in combination with diabetes is associated with an earlier rise in L/S ratio. A poor correlation of L/S ratio and neonatal pulmonary outcome with birthweight and gestational age was found. However, a good correlation between L/S ratio and neonatal pulmonary outcome was apparent. An L/S ratio of over 2 was universally associated with absence of serious RDS, but a low L/S ratio was less precisely predictive.