Objective: To assess the color Doppler flow velocity pattern of Aortic isthmus in fetuses with intra uterine growth restriction.To found the association of Aortic isthmus Doppler flow parameters and intra uterine growth restriction. Introduction: Fetal medicine has very crucial role in management of Intra-uterine growth restriction (IUGR), which is an important perinatal problem of morbidity and mortality of fetus. Fetal medicine helps to establish early diagnosis and timely intervention in undergoing to develop IUGR and already developed IUGR. Doppler imaging is very important tool to obtain this information and very effective than any other conventional tests. The Doppler has ability to guide management decisions regarding the appropriate timing of delivery.Doppler imaging of Aortic isthmus (AoI) has proposed potential monitoring tool for IUGR fetus. The AoI is an arterial connection between the two fetal vascular outputs positioned in parallel and acts as a link between the right and left ventricles. So, any condition affecting fetal hemodynamic involving ventricular outflow or peripheral vascular impedance will affect the flow pattern through AoI. Material and methods: This descriptive comparative study was performed on fetuses with suspected IUGR over a period of 24 months. 50 pregnant females of 24-40 weeks gestation who presented to OPD met the inclusion criteria. The fetuses, those are small for gestational age and had associated maternal pathologies/risk factors, abnormal umbilical artery Doppler waveforms and oligohydramnios were considered as cases. The parameters of cases compared with 50 controls, selected randomly from the referred healthy pregnant females. The role of Aortic isthmus Doppler indices (PI, RI, PSV, EDV) and of a semi-quantitative indicator (Isthmic Flow Index, IFI) was assessed in predicting IUGR by using sensitivity, specificity and predictive values. P-value of <0.05 was considered to be significant. Results: 29 out of 50 fetuses had IFI value < 1 suggesting reversed isthmic diastolic blood flow and 21 out of 50 had forward flow with IFI > 1. Mean RI and PI value in cases were 1.1354(+/- 0.23) and 7.5392(+/- 8.80), respectively which was significantly higher as compared to mean RI of 0.8086(+/- 0.099) (P-value <0.0001) and mean PI value of 2.6154(+/- 1.064) (P-value = 0.0002) in control cohort. Aortic isthmus PI value above 95th centile was found in 33/50 (66%) of cases. 7/50 (14%) cases had retrograde AoI flow while the umbilical artery Doppler indices were normal. Conclusion: PI and RI values of aortic isthmus in the IUGR fetuses were found to be significantly higher as compared to those in controls. The study parameters and analyzed outcome suggests association of reversed diastolic flow through AoI with IUGR.