Study was performed on 40 cases (10 normal full term pregnanciesand 30 high risk patients) , five items of sonographic prediction offetal lung maturity (composite age, placental grade, amniotic fluidturbidity, lung/liver ratio and distal femoral epiphysis) correlated todevelopment of respiratory distress syndrome (RDS) in newborns.Statistical analysis of results found that RSD is more predicted withsmall femur length (FL) measurement, and using 7.3 cm cut off pointfor FL is a good predictor for fetal lung maturity with sensitivity 86%and specificity 84% in our study.