Amniotic fluid lecithin/sphingomyelin ratio as an assessment of fetal pulmonary maturity

Abstract

The method of Gluck and associates1 for estimating the lecithin/sphingomyelin ratio in amniotic fluid has proved to have a high degree of accuracy in predicting fetal lung maturity. One hundred and eighty-five samples of amniotic fluid from 167 patients in various weeks of gestation were assayed. A lecithin/sphingomyelin (L/S) ratio of 1.5 or less indicated an immature fetal lung, and, in all spontaneously delivered infants, where the values were in this range, the infant developed the respiratory distress syndrome (RDS) and hyaline membrane disease. An L/S ratio of 1.51 to 1.80 suggested a transitional fetal lung in which some of the infants developed RDS, and possibly a mild hyaline membrane disease, but all recovered. If the L/S ratio was over 1.80, the lung was considered to be mature for normal function in the external evironment, and respiratory distress did not develop. The L/S ratio in amniotic fluid is a rapid, accurate method to assess fetal lung maturity and is an invaluable aid in the management of increased risk pregnancies and in cases of repeat cesarean section where the gestational age is unknown.