Lecithin:sphingomyelin ratio in pregnancies complicated by insulin-dependent diabetes mellitus

One hundred forty-one samples of amniotic fluid in 105 pregnancies from 95 insulin-dependent diabetics were analyzed for the lecithin:sphingomyelin (L:S) ratio. Fetal pulmonary maturity seemed to progress at a normal rate. The mean L:S ratio was not significantly different in diabetic and nondiabetic patients at various stages of gestation. Only 3 cases of respiratory distress syndrome (RDS) were observed in 77 infants with an L:S ratio of 2.0 or more delivered of diabetic mothers within 72 hours of amniocentesis. This 3.9% incidence of RDS in infants of diabetic mothers with L:S ratios of more than 2.0 was not significantly higher than the 1.5% incidence in the nondiabetic mothers. It is concluded that by using the method of Gluck, an L:S ratio of 2.0 or greater at 36 weeks' gestation or later is a reliable indicator of fetal lung maturity in insulin-dependent diabetic pregnancies, and abdominal delivery after 36 weeks' gestation does not increase the risk of RDS in a diabetic pregnancy with an L:S ratio at 2.0 or more.