Correlation of optical density, lecithin and lecithin/sphingomyelin ratio in amniotic fluid

The correlation between optical density at 650 nm, lecithin and lecithin/sphingomyelin ration was investigated in 94 amniotic fluid samples obtained from 90 patients between 28 and 40 weeks of pregnancy. All samples were processed immediately and those contaminated with blood or meconium were discarded. The correlation coefficient between lecithin and absorbance was high (0.926). The lecithin/sphingomyelin ratio also had a good correlation coefficient with the optical density (0.768). We conclude that absorbance at 650 nm is a reliable test for assessing fetal lung maturation.