Abstract Background: The utility of non invasive tests for lung maturity should be encouraged for better timing of delivery in the risky groups especially diabetic patients. Aim of Study: To evaluate fetal pulmonary artery indices in Diabetic mothers near delivery and further changes in response to corticosteroid therapy. Patients and Methods: Multi step study was done, step one (case-control study) includes: Assessment of Pulmonary Artery Indices in groups (A) normal in comparison to group (B) Diabetic mothers. Step two (cross sectional study) on the Diabetic group only to assess the impact of steroid exposure on Doppler indices. Step three: Follow them postnatal to reveal the best cutoff values predicting respiratory distress syndrome RDS in neonates. Results: The pulmonary indices (PI, RI) are much higher in diabetic patients, However (AT/ET) is significantly lower in the same group & marvelous improvement after steroid dose. The best cutoff value for AT/ET in predicting RDS (0.28) sensitivity, specificity & accuracy (81.3%, 96.5% & 94%) respectively. Conclusions: Pulmonary artery indices are valuable and promising predictor for lung maturity in Diabetic patients.