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Updated: Sep 25, 2026
Human Fetal Blood Flow Quantification with Magnetic Resonance Imaging and Motion Compensation
Published on: January 7, 2021
Reference values for an index of fetal aortic isthmus blood flow during the second half of pregnancy
J Ruskamp1, J-C Fouron, J Gosselin
1Fetal Cardiology Unit, Pediatric Cardiology Service, Department of Pediatrics, Ste-Justine Hospital, University of Montreal, Quebec, Canada.
Objective:
During fetal life, the parallel position of the two cardiac ventricles confers a special status to the aortic isthmus. Flow through the isthmus reflects the balance between the performances of the two ventricles and their respective peripheral impedances. This study proposes a fetal aortic isthmus flow velocity index and its reference values defined on the basis of gestational age (GA).
Methods:
Video recordings of 111 normal fetuses from 18 to 39 weeks of gestation were retrospectively reviewed. An isthmus flow velocity index (IFI) was calculated as follows: IFI = (systolic + diastolic)/systolic velocity integrals. GA-specific reference ranges of IFI were constructed.
Results:
An IFI of 1.33 +/- 0.03 was found at 18 weeks. This value decreased slightly but steadily with GA to reach 1.23 +/- 0.16 at 39 weeks. This change is mainly related to a decrease in diastolic velocity integrals.
Conclusion:
The proposed IFI provides information on the direction and, indirectly, on the volume of blood flow through the fetal aortic isthmus.
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