Amniotic fluid absorbance at 650 nm: A comparison with fetal lung maturity characteristics

Using the rhesus monkey as an animal model we measured several indices of fetal lung maturation including pressure-volume characteristics and phospholipid concentrations and correlated them with the absorbance of amniotic fluid at 650 nm (A₆₅₀). Those parameters, which are indicative of the presence of surfactant (i.e., deflation stability, lecithin-sphingomyelin ratio, lung phosphatidylcholine, as well as disaturated phosphatidylcholine), correlate significantly with the amniotic fluid A₆₅₀, even after correction for gestational age. Maximal lung volume changes, thought to be reflective of alterations in tissue forces, did not correlate with A₆₅₀. These data in the rhesus fetus indicate that the A₆₅₀ reflects pulmonary surfactant characteristics independent of gestational age. Accordingly, this test may prove to be an accurate predictor of the risk of the respiratory distress syndrome.