Background: Fetal lung maturity assessment is regarded as the most critical factor for identifying the optimal delivery time. A noninvasive sonographic technique is necessary to evaluate fetal lung development, as amniocentesis is an invasive method that result in real hazard to pregnancy.
Aim of the study: This study aimed to predict maturity of fetal lung utilizing 3D lung volume ultrasound, lung to liver intensity ratio, and pulmonary artery Doppler indices measurement.
Patients and Methods: Three-dimensional [3D] ultrasound [3DUS] has been performed to determine the fetal lung volume [FLV] then fetal lung-to-liver intensity ratio [FLLIR] [tissue histogram] and the main pulmonary artery doppler parameters [MPA]; acceleration time-to-ejection timer ratio [At/Et], pulsatility index [PI] and resistive index [RI] have been performed to two hundred pregnant females from thirty-two to forty weeks age at pregnancy during one week from delivery. 
Results: Of 200 fetuses investigated, 113 cases [56.5%] have been investigated with respiratory distress syndrome. The MPA RI and PI were significantly greater in fetuses investigated with respiratory distress syndrome comparing with those with no [2.6± 0.3 and 0.9±0.05 vs. 1.9±0.3 and 0.8±0.2, p-value less than 0.001, less than 0.001 respectively]. MPA At/Et was significantly lesser for fetuses with RDS than fetuses without RDS [0.2±0.1 vs. 0.3±0.1 respectively, p-value less than 0.001]. FLLIR was significantly lesser in RDS positive group comparing with RDS negative group [0.9±0.2 versus 1.3±0.3 respectively, p-value less than 0.001] and FLV was significantly smaller in fetuses with respiratory distress syndrome comparing with those with no [31.5±2.5 vs. 38.1±2.8; p-value less than 0.001].
Conclusion: The utilization of main pulmonary artery Doppler indices, together with mean fetal lung volume and FLLIR for assessing fetal lung is a quick noninvasive accurate technique for estimate of neonatal FLM and respiratory distress syndrome.