Severity of respiratory distress syndrome with low lecithin: sphingomyelin ratio.

The frequency and severity of respiratory distress syndrome (RDS) were evaluated in 69 infants whose amniotic fluid lecithin: sphingomyelin (L:S) ratio was less than 2. Amniotic fluid was obtained at the time of either nonelective or elective cesarean section in 58 cases. An additional 11 patients were delivered within 48 hours after amniocentesis. Gestational ages ranged from 27 to 41 weeks. Few women had been in labor, none had ruptured membranes for more than 12 hours, and all but 3 were delivered by cesarean section. A variety of pregnancy complications were represented. All 14 infants with an L:S ratio less than 0.5 developed RDS, and 10 died. Of 19 infants with an L:S ratio of 0.5 to 0.99, 8 developed RDS; 3 of the 8 died and another 3 required ventilatory support. Of 36 infants whose L:S ratio exceeded 1.0, only 1 developed RDS. No infant who had an L:S ratio greater than 0.8 died of RDS, and RDS was absent in infants with L:S ratio as low as 0.6. These findings could not be attributed to intraassay or interassay variability or to laboratory methodology. The importance of individual laboratory evaluation of L:S values in relation to respiratory outcome is emphasized.