Background: incubation with sildenafil citrate limits the effects of vasoconstrictors on myometrial small arteries of normal pregnancy women and pregnant women with fetal growth restriction. So that phosphodiesterase inhibitors seem to improve uterine perfusion safely in pregnancies with fetal growth restriction. Objective: the main aim of this study was to demonstrate the effect of sildenafil citrate when added to low dose aspirin and low molecular weight heparin on the uterine and umbilical artery Doppler to improve neonatal outcome in patients with high-risk pregnancy. Subjects and Methods: The study was conducted at Al-Azhar University Hospitals, Cairo, Egypt. From March 2017 to January 2019. One hundred patients (50 in each arm of the study), who had or have a high-risk pregnancy, were selected and enrolled into a randomized clinical trial. Results: there was significant increase in amniotic fluid index (AFI) and umbilical artery Doppler parameters. Group B (heparin/aspirin) also showed significant improvement in fetal biometry and Doppler parameters but when comparing the differences between the two groups, none of these changes were statistically significant except for the femur length measurement and the uterine artery resistance index. Conclusion: from the results of our study we concluded that heparin and aspirin combination or when sildenafil is also added have beneficial effects in the treatment of pregnant women whom vascular impairment is expected showing improvement in the fetal growth parameters and reduction of admission.