Most laboratory tests for fetal lung maturity (FLM) are optimized to exclude false-negative predictions of absence of respiratory distress syndrome (RDS), with a reciprocal low predictive value for maturity. The authors employed FLM Surfactant/Albumin Ratio (FLM S/A) test results to construct a predictive model for FLM that included the obstetric estimates of gestational age. The charts of 388 newborns were abstracted and reviewed. The clinical outcome was the gold standard of the multivariate logistic analysis. Both the obstetric estimates of gestational age and the test result were significant predictors of the clinical outcome (P values of < .0002 and .001, respectively). The prediction rule for RDS as a function of both of these variables allows for adjustment of the test cutoffs, so that there is a consistent probability of RDS at the cutoff FLM S/A result for different gestational ages. Fetal lung maturity probability reporting may facilitate clinical decision-making.