Lung maturity tests: Relation to source, clarity, gestational age and neonatal outcome

OBJECTIVE: To determine whether gestational age is a significant determinant of neonatal outcome, irrespective of biochemical lung maturity. The effects of specimen source and clarity on the reliability of biochemical tests for predicting respiratory distress syndrome are also evaluated. STUDY DESIGN: Perinatal outcome was analyzed for 904 neonates undergoing amniotic fluid maturity studies within three days of delivery from 1991 to 1993. The relationships of gestational age and biochemical maturity to neonatal outcome were examined using multivariate analysis of covariance. Test reliability was evaluated using log-linear analysis of multiway frequency tables. RESULTS: Gestational age was a better predictor of neonatal outcome than biochemical lung maturity. Gestational age significantly correlated with every measure of outcome except intraventricular hemorrhage and jaundice. Test reliability was not significantly influenced by specimen source or clarity. CONCLUSION: Results obtained using contaminated amniotic fluid are reliable when the proper technique is used. Irrespective of biochemical maturity, neonatal outcome is significantly related to gestational age. Gestational age, and not just biochemical maturity, should be considered when timing delivery.