Lamellar body phospholipid content of amniotic fluid and L/S ratio compared in assessing fetal lung maturity

A micro-method has been devised for isolating a lung-derived membranous fraction from human amniotic fluid. The phospholipid content of this fraction, known as lamellar body phospholipid, provides an indication of fetal lung maturity (Ann. Clin. Biochem 16: 191, 1979). This method has now been applied to 479 samples of amniotic fluid from 330 pregnancies. The lecithin/sphingomyelin ratio has also been determined for each of the samples by the routine method currently in use in the hospitals providing the samples. Hyaline membrane disease was associated with a low concentration of lamellar body phospholipid (less than 35 mg/L) in all eight cases encountered in this study. In contrast, in 182 of the 185 cases where the lamellar body content of the amniotic fluid, collected within two days of delivery, exceeded 35 mg/L, the infants were free from serious respiratory problems. Data are presented which suggests that the lecithin/sphingomyelin ratio falsely indicated lung immaturity in many cases, amounting to 44% or more of all values indicating immaturity that were reported.