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.