title: The hemodynamics of late-onset intrauterine growth restriction by MRI.
abstract: BACKGROUND
  Late-onset intrauterine growth restriction (IUGR) results from a failure of the placenta to supply adequate nutrients and oxygen to the rapidly growing late-gestation fetus. Limitations in current monitoring methods present the need for additional techniques for more accurate diagnosis of IUGR in utero. New magnetic resonance imaging (MRI) technology now provides a noninvasive technique for fetal hemodynamic assessment, which could provide additional information over conventional Doppler methods.
  
  
  OBJECTIVE
  The objective of the study was to use new MRI techniques to measure hemodynamic parameters and brain growth in late-onset IUGR fetuses.
  
  
  METHODS
  This was a prospective observational case control study to compare the flow and T2 of blood in the major fetal vessels and brain imaging findings using MRI. Indexed fetal oxygen delivery and consumption were calculated. Middle cerebral artery and umbilical artery pulsatility indexes and cerebroplacental ratio were acquired using ultrasound. A score of ≥ 2 of the 4 following parameters defined IUGR: (1) birthweight the third centile or less or 20% or greater drop in the centile in estimated fetal weight; (2) lowest cerebroplacental ratio after 30 weeks less than the fifth centile; (3) ponderal index < 2.2; and (4) placental histology meets predefined criteria for placental underperfusion. Measurements were compared between the 2 groups (Student t test) and correlations between parameters were analyzed (Pearson's correlation). MRI measurements were compared with Doppler parameters for identifying IUGR defined by postnatal criteria (birthweight, placental histology, ponderal index) using receiver-operating characteristic curves.
  
  
  RESULTS
  We studied 14 IUGR and 26 non-IUGR fetuses at 35 weeks' gestation. IUGR fetuses had lower umbilical vein (P = .004) and pulmonary blood flow (P = .01) and higher superior vena caval flow (P < .0001) by MRI. IUGR fetuses had asymmetric growth but smaller brains than normal fetuses (P < .0001). Newborns with IUGR also had smaller brains with otherwise essentially normal findings on MRI. Vessel T2s, oxygen delivery, oxygen consumption, middle cerebral artery pulsatility index, and cerebroplacental ratio were all significantly lower in IUGR fetuses, whereas there was no significant difference in umbilical artery pulsatility index. IUGR score correlated positively with superior vena caval flow and inversely with oxygen delivery, oxygen consumption, umbilical vein T2, and cerebroplacental ratio. Receiver-operating characteristic curves revealed equivalent performance of MRI and Doppler techniques in identifying IUGR that was defined based on postnatal parameters with superior vena caval flow area under the curve of 0.94 (95% confidence interval, 0.87-1.00) vs a cerebroplacental ratio area under the curve of 0.80 (95% confidence interval, 0.64-0.97).
  
  
  CONCLUSIONS
  MRI revealed the expected circulatory redistribution in response to hypoxia in IUGR fetuses. The reduced oxygen delivery in IUGR fetuses indicated impaired placental oxygen transport, whereas reduced oxygen consumption presumably reflected metabolic adaptation to diminished substrate delivery, resulting in slower fetal growth. Despite brain sparing, placental insufficiency limits fetal brain growth. Superior vena caval flow and umbilical vein T2 by MRI may be useful new markers of late-onset IUGR.
authors.affiliation: Institute of Medical Science, University of Toronto, Toronto, ON, Canada; Division of Cardiology, Mount Sinai Hospital, University of Toronto, ON, Canada.
authors.forename: Meng Yuan
authors.initials: MY
authors.lastname: Zhu
authors.affiliation: Department of Obstetrics and Gynecology, Mount Sinai Hospital, University of Toronto, Toronto, ON, Canada.
authors.forename: Natasha
authors.initials: N
authors.lastname: Milligan
authors.affiliation: Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, University of Toronto, Toronto, ON, Canada.
authors.forename: Sarah
authors.initials: S
authors.lastname: Keating
authors.affiliation: Department of Obstetrics and Gynecology, Mount Sinai Hospital, University of Toronto, Toronto, ON, Canada.
authors.forename: Rory
authors.initials: R
authors.lastname: Windrim
authors.affiliation: Division of Maternal-Fetal Medicine, Mount Sinai Hospital, University of Toronto, Toronto, ON, Canada.
authors.forename: Johannes
authors.initials: J
authors.lastname: Keunen
authors.affiliation: Division of Cardiology, Mount Sinai Hospital, University of Toronto, ON, Canada.
authors.forename: Varsha
authors.initials: V
authors.lastname: Thakur
authors.affiliation: Division of Cardiology, Mount Sinai Hospital, University of Toronto, ON, Canada.
authors.forename: Annika
authors.initials: A
authors.lastname: Ohman
authors.affiliation: Departments of Physiology and Experimental Medicine, Mount Sinai Hospital, University of Toronto, ON, Canada.
authors.forename: Sharon
authors.initials: S
authors.lastname: Portnoy
authors.affiliation: Departments of Physiology and Experimental Medicine, Mount Sinai Hospital, University of Toronto, ON, Canada.
authors.forename: John G
authors.initials: JG
authors.lastname: Sled
authors.affiliation: Division of Neonatology, Department of Paediatrics, Mount Sinai Hospital, University of Toronto, ON, Canada.
authors.forename: Edmond
authors.initials: E
authors.lastname: Kelly
authors.affiliation: Division of Cardiology, Mount Sinai Hospital, University of Toronto, ON, Canada.
authors.forename: Shi-Joon
authors.initials: SJ
authors.lastname: Yoo
authors.affiliation: Division of Cardiology, Mount Sinai Hospital, University of Toronto, ON, Canada.
authors.forename: Lars
authors.initials: L
authors.lastname: Gross-Wortmann
authors.affiliation: Division of Cardiology, Mount Sinai Hospital, University of Toronto, ON, Canada.
authors.forename: Edgar
authors.initials: E
authors.lastname: Jaeggi
authors.affiliation: Departments of Physiology and Experimental Medicine, Mount Sinai Hospital, University of Toronto, ON, Canada.
authors.forename: Christopher K
authors.initials: CK
authors.lastname: Macgowan
authors.affiliation: Department of Obstetrics and Gynecology, Mount Sinai Hospital, University of Toronto, Toronto, ON, Canada.
authors.forename: John C
authors.initials: JC
authors.lastname: Kingdom
authors.affiliation: Institute of Medical Science, University of Toronto, Toronto, ON, Canada; Division of Cardiology, Mount Sinai Hospital, University of Toronto, ON, Canada. Electronic address: mike.seed@sickkids.ca.
authors.forename: Mike
authors.initials: M
authors.lastname: Seed
mesh_terms: D000328:Adult; D019540:Area Under Curve; D001724:Birth Weight; D001921:Brain / Q000196:embryology*; D016022:Case-Control Studies; D002560:Cerebrovascular Circulation; D005260:Female; D005317:Fetal Growth Retardation / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000503:physiopathology*; D006439:Hemodynamics; D006801:Humans; D007231:Infant, Newborn; D008279:Magnetic Resonance Imaging; D020768:Middle Cerebral Artery / Q000000981:diagnostic imaging / Q000502:physiology; D010100:Oxygen / Q000378:metabolism; D010101:Oxygen Consumption; D010920:Placenta / Q000098:blood supply / Q000473:pathology; D021041:Placental Circulation; D011247:Pregnancy; D011263:Pregnancy Trimester, Third / Q000502:physiology; D011446:Prospective Studies; D011673:Pulsatile Flow; D012372:ROC Curve; D012039:Regional Blood Flow; D018608:Ultrasonography, Doppler; D014469:Umbilical Arteries / Q000000981:diagnostic imaging / Q000502:physiology; D014683:Vena Cava, Superior / Q000000981:diagnostic imaging / Q000502:physiology
chemical_list: D010100:Oxygen
keywords: Doppler; fetus; intrauterine growth restriction; magnetic resonance imaging; small for gestational age