title: Reference values for an index of fetal aortic isthmus blood flow during the second half of pregnancy.
abstract: 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.
  
  
  CONCLUSIONS
  The proposed IFI provides information on the direction and, indirectly, on the volume of blood flow through the fetal aortic isthmus.
authors.affiliation: Fetal Cardiology Unit, Pediatric Cardiology Service, Department of Pediatrics, Ste-Justine Hospital, University of Montreal, Quebec, Canada.
authors.forename: J
authors.initials: J
authors.lastname: Ruskamp
authors.forename: J-C
authors.initials: JC
authors.lastname: Fouron
authors.forename: J
authors.initials: J
authors.lastname: Gosselin
authors.forename: M-J
authors.initials: MJ
authors.lastname: Raboisson
authors.forename: C
authors.initials: C
authors.lastname: Infante-Rivard
authors.forename: F
authors.initials: F
authors.lastname: Proulx
mesh_terms: D001013:Aorta, Thoracic / Q000196:embryology / Q000502:physiology*; D001783:Blood Flow Velocity / Q000502:physiology; D005260:Female; D005865:Gestational Age; D006801:Humans; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011263:Pregnancy Trimester, Third; D012016:Reference Values; D012189:Retrospective Studies; D014741:Video Recording