Comparison of two tests and absorbance at 650 nm for assessing fetal lung maturity.

The clinical performance of three rapidly performed tests--tap test, TDx Fetal Lung Maturity and amniotic fluid absorbance at 650 nm--in predicting fetal lung maturity were evaluated in 300 samples of clear amniotic fluid. In all cases, delivery occurred within three days of sample collection. Of the 300 newborns, 44 developed respiratory distress syndrome. For the tap test, the sensitivity (95.4%), specificity (82.8%), and predictive value for maturity (99.7%) and immaturity (48.9%) were comparable to those of the TDx fetal lung maturity test: sensitivity of 100%, specificity of 88.3%, and predictive value for maturity of 100% and immaturity of 53.1%. The specificity (68.4%) and predictive value for immaturity (34.7%) of amniotic fluid absorbance at 650 nm were significantly lower than for the TDx and tap tests, whereas no significant difference was found for sensitivity and prediction of maturity between amniotic fluid absorbance at 650 nm and the TDx and tap tests. Both the tap and the TDx tests appear to be useful in antenatal assessment of fetal lung maturity in terms of reliability, rapidity and uniformity.