title: Proton magnetic resonance spectroscopy assessment of fetal brain metabolism in late-onset 'small for gestational age' versus 'intrauterine growth restriction' fetuses.
abstract: OBJECTIVE
  We used magnetic resonance spectroscopy (MRS) to evaluate brain metabolic differences in small fetuses near term as compared to appropriate for gestational age (AGA) fetuses.
  
  
  METHODS
  71 term small fetuses (estimated fetal weight <10th centile for gestational age with normal umbilical artery Doppler sonography) were subclassified as late intrauterine growth restriction (IUGR) (n = 50) or small for gestational age (SGA) (n = 21), and compared with 65 AGA fetuses. IUGR was defined by either abnormal middle cerebral artery, abnormal uterine artery Doppler sonography or estimated fetal weight <3rd centile. All participants underwent brain magnetic resonance imaging at 37 weeks of gestation, and single-voxel magnetic resonance spectra were obtained from the frontal lobe on a 3-tesla scanner. N-acetylaspartate (NAA)/choline (Cho), NAA/creatine (Cr) and Cho/Cr ratios were calculated and compared between cases and controls. The association of the metabolic ratios with the study groups was tested.
  
  
  RESULTS
  After MRS processing and applying quality control criteria, 31 spectra from late-onset IUGR, 11 from SGA and 30 from AGA fetuses were selected for further analysis. Both SGA and late-onset IUGR fetuses showed significantly reduced NAA/Cho levels when compared to AGA fetuses. This decrease followed a linear trend across the three clinical groups that were considered.
  
  
  CONCLUSIONS
  Both SGA and late-onset IUGR fetuses showed differences in MRS brain metabolic ratios. The findings suggest that despite near-normal perinatal outcomes, SGA fetuses are not constitutionally small and may represent a form of growth disorder that needs to be clarified.
authors.affiliation: Maternal-Fetal Medicine Department, Instituto Clínic de Ginecologia, Obstetrica y Neonatología, Hospital Clínic, Universitat de Barcelona, Barcelona, Spain.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Sanz-Cortes
authors.forename: Rui V
authors.initials: RV
authors.lastname: Simoes
authors.forename: Nuria
authors.initials: N
authors.lastname: Bargallo
authors.forename: Narcis
authors.initials: N
authors.lastname: Masoller
authors.forename: Francesc
authors.initials: F
authors.lastname: Figueras
authors.forename: Eduard
authors.initials: E
authors.lastname: Gratacos
mesh_terms: D000328:Adult; D001921:Brain / Q000196:embryology* / Q000378:metabolism*; D015331:Cohort Studies; D005260:Female; D005317:Fetal Growth Retardation / Q000175:diagnosis* / Q000378:metabolism*; D005500:Follow-Up Studies; D006801:Humans; D007231:Infant, Newborn; D007236:Infant, Small for Gestational Age / Q000378:metabolism*; D011247:Pregnancy; D011446:Prospective Studies; D066244:Proton Magnetic Resonance Spectroscopy; D055815:Young Adult