Lecithin/sphingomyelin ratio in amniotic fluid and its value for the prediction of neonatal respiratory distress syndrome in pregnant diabetic women

In 101 diabetic pregnant women (Classes A through D) 146 determinations of the lecithin/sphingomyelin ( L/S ) ratio were carried out. Gestational ages were verified by serial fetal cephalometry. No L/S ratios of more than 2.0 were found before 341/2 weeks' gestation; however, in 42 per cent of patients the L/S ratio was below 2.0 at 36 weeks' gestation or later. Respiratory distress syndrome (RDS) was found in 16 neonates of women with L/S ratios of 2.0 or higher; however, RDS incidence varied depending on the mode of delivery. Abdominal delivery was performed before 37 weeks' gestation in 19 patients with L/S ratios of 2.0 or higher and resulted in neonates with RDS in 41 per cent of cases. Vaginal delivery was accomplished before 37 weeks' gestation in 10 patients with L/S ratios of 2.0 or higher and no subsequent neonatal RDS was observed. After 37 weeks' gestation neonatal RDS is rare, irrespective of mode of delivery. The data presented suggest that similar numerical values of the L/S ratio at different gestational ages have a different predictive value for the occurrence of neonatal RDS.