title: Absence of PO2 change in fetal brain despite PO2 increase in placenta in response to maternal oxygen challenge.
abstract: OBJECTIVE
  Magnetic resonance imaging allows the noninvasive observation of PO2 changes between air breathing and oxygen breathing through quantification of the magnetic longitudinal relaxation time T1. Changes in PO2 are proportional to changes in the longitudinal relaxation rate ΔR1 (where ΔR1=1/T1oxygen-1/T1air). Knowledge of this response could inform clinical interventions using maternal oxygen administration antenatally to treat fetal growth restriction. We present in vivo measurements of the response of the fetal-placental unit to maternal hyperoxia.
  
  
  METHODS
  Prospective cohort.
  
  
  METHODS
  Large tertiary maternity hospital.
  
  
  METHODS
  Nine women undergoing low-risk pregnancy (21-33 weeks of gestation) and five nonpregnant adults.
  
  
  METHODS
  During imaging the air supply to mothers was changed from medical air (21% oxygen) to medical oxygen (100% oxygen) and T1 was monitored over time in both the placenta and fetal brain using a periodically repeated magnetic resonance imaging sequence. To demonstrate that the method could detect a brain response, brain responses from five normal adult volunteers were measured using a similar imaging protocol.
  
  
  METHODS
  Changes in T1 following oxygen challenge.
  
  
  RESULTS
  No significant ΔR1 (P=0.42, paired t-test) was observed in fetal brains. A significant placental ΔR1 (P=0.0002, paired t-test) of 0.02±0.01/s (mean±SD) was simultaneously observed in the same participants. In the brains of the nonpregnant adults, a significant ΔR1 (P=0.01, paired t-test) of 0.005±0.002/s was observed.
  
  
  CONCLUSIONS
  Short-term maternal oxygen administration does not improve fetal brain oxygenation, in contrast to the response observed in the adult brain.
authors.affiliation: Centre for Imaging Sciences, University of Manchester, Manchester, UK; The University of Manchester Biomedical Imaging Institute, University of Manchester, Manchester, UK.
authors.forename: I
authors.initials: I
authors.lastname: Huen
authors.forename: D M
authors.initials: DM
authors.lastname: Morris
authors.forename: C
authors.initials: C
authors.lastname: Wright
authors.forename: C P
authors.initials: CP
authors.lastname: Sibley
authors.forename: J H
authors.initials: JH
authors.lastname: Naish
authors.forename: E D
authors.initials: ED
authors.lastname: Johnstone
mesh_terms: D000328:Adult; D001921:Brain / Q000378:metabolism*; D015331:Cohort Studies; D005260:Female; D005333:Fetus / Q000378:metabolism*; D006801:Humans; D018496:Hyperoxia / Q000378:metabolism*; D008279:Magnetic Resonance Imaging; D010100:Oxygen / Q000378:metabolism*; D010102:Oxygen Inhalation Therapy; D010313:Partial Pressure; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011263:Pregnancy Trimester, Third; D011446:Prospective Studies; D055815:Young Adult
chemical_list: D010100:Oxygen
keywords: Brain; fetus; longitudinal relaxation rate; magnetic resonance imaging; oxygen; placenta; pregnancy