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Abstract Corticosteroid administration before anticipated preterm birth is a well known antenatal therapy available to improve newborn outcomes. Doppler studies of maternal and foetal vessels provide a way to understand how corticosteroid affects and improves foetal respiratory outcome. This study was registered on 8th of October, 2017 by Menoufia Faculty of Medicine Board with registration number 222-2-10-2017. It included 80 pregnant women divided into two groups. Each group consisted of 40 participants. Group A: participants were between 28 weeks and 34 weeks of gestation and were at risk of preterm labour. Group B: participants were those who had undergone an elective caesarean section (CS) before completing the 39th week of gestation. Each woman had received four doses of Dexamethasone 6 mg intramuscularly, 12 h apart. Doppler studies were performed before the Dexamethasone adminstration and 24 h after the Dexamethasone course. Among both groups, only pregnant women before 34 weeks of gestation showed a significant decrease in middle cerebral artery pulsatility index. However, the other Doppler parameters showed no significant effect. In conclusion, Dexamethasone administration affected only the middle cerebral artery pulsatility index before 34 weeks of gestation. IMPACT STATEMENT What is already known on this subject? Preterm births account for 75% of neonatal morbidity and pulmonary dysfunction plays an important role on such morbidities. Also, neonates born after an elective CS have significantly higher rates of respiratory morbidity and neonatal intensive care unit admission. Corticosteroids are wildly used to improve neonatal outcome in women who have expected preterm labour and before an elective CS. What do the results of this study add? Dexamethasone affected blood distribution of foetal brain only before 34 weeks of gestation that had been proved by changes of foetal middle cerebral artery pulsatility index without affecting other Doppler parameters of both groups. With the improvement of foetal respiratory outcome in both groups. What are the implications of these finding for clinical practice and/or further research? Maternal Dexamethasone injection is recommended for mothers at risk of preterm labour, especially if delivery is expected within six days and mothers who will undergo elective CS before completion of 39 weeks of gestation, in terms of improving neonatal respiratory functions and decreasing the possibility of admission to neonatal intensive care unit for transient tachypnoea of the newborn.