الفهرس 
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Abstract
The aortic isthmus (AoI) is a unique fetal watershed with a waveform reflecting its complex hemodynamic physiology. [11]
Several indices have been devised to quantify different components of the waveform, including the pulsatility index, resistance index, isthmic flow index, and recently the isthmic systolic index. There have been promising preliminary studies applying these indices to both cardiac (congenital) and extracardiac pathologies, including intrauterine growth restriction and twin-twin transfusion syndrome. [11]
Our study aims to establish reference ranges for blood flow velocity waveforms (FVW) of the fetal aortic isthmus (AoI) among women attending women’s health hospital of Assiut university.
Our study showed that AoI-PI ranged from 0.87 to 11.14 with a mean of 2.34± 1.13, while the AoI-RI ranged from 0.40 to 8.60 with a mean of 0.93± 0.49.
When referring to the reference gestational-age-related doppler parameters (PI & RI) in the AoI, at gestational age 28 weeks, which was the mean gestational age in our study, the reference AoI-PI was 2.76, while the reference AoI-RI was 1.35. [4]
A regression analysis for PI and RI with advancing gestation showed a significant increase in PI (r=0.12, p=0.022), and a significant weak increase in RI (r=0.11, p=0.037).
This was partly in agreement with several studies, and reflective of our population in question.