title: Thymic volume in healthy, small for gestational age and growth restricted fetuses.
abstract: OBJECTIVE
  The aim of this study was to verify the hypothesis that a difference in thymic size exists between small for gestational age (SGA) fetuses, likely constitutional, and intrauterine growth restricted (IUGR) fetuses because of placental causes.
  
  
  METHODS
  We studied 27 SGA and 36 control fetuses. SGA was defined as fetal abdominal circumference (AC) and birthweight <10th percentile for gestational age. We defined as constitutional SGA those with normal uterine and umbilical artery Doppler flow velocity waveforms (FVW), and as IUGR those with abnormal uterine FVW. IUGR were further divided based on normal or abnormal umbilical FVW. Fetal thymic volume (TV) was acquired by three-dimensional ultrasound and reconstructed with virtual organ computer-aided analysis. To correct for the influence of fetal size on thymic dimension, TV/AC ratio was calculated.
  
  
  RESULTS
  Controls presented a higher TV/AC compared with each group of SGA (p < 0.001). TV/AC was significantly lower in IUGR with abnormal umbilical FVW compared with both constitutional SGA (p = 0.01) and IUGR with normal umbilical FVW (p = 0.01).
  
  
  CONCLUSIONS
  The differences in TV/AC between constitutional SGA and IUGR with abnormal umbilical FVW suggest that, in the latter, a specific 'trigger' might compromise trophoblastic invasion and thymic development; however, some kind of alteration of the immune system might occur in all SGA fetuses.
authors.affiliation: Department of Obstetrics and Gynecology, University of Turin, Turin, Italy. olearo.elena85@libero.it
authors.forename: Elena
authors.initials: E
authors.lastname: Olearo
authors.forename: Manuela
authors.initials: M
authors.lastname: Oberto
authors.forename: Giovanna
authors.initials: G
authors.lastname: Oggè
authors.forename: Giovanni
authors.initials: G
authors.lastname: Botta
authors.forename: Carlotta
authors.initials: C
authors.lastname: Pace
authors.forename: Pietro
authors.initials: P
authors.lastname: Gaglioti
authors.forename: Tullia
authors.initials: T
authors.lastname: Todros
mesh_terms: D016022:Case-Control Studies; D003430:Cross-Sectional Studies; D005260:Female; D005317:Fetal Growth Retardation / Q000473:pathology*; D005333:Fetus / Q000033:anatomy & histology* / Q000473:pathology*; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D007236:Infant, Small for Gestational Age; D009929:Organ Size; D010920:Placenta / Q000000981:diagnostic imaging; D011247:Pregnancy; D011446:Prospective Studies; D013950:Thymus Gland / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000473:pathology*; D016216:Ultrasonography, Prenatal; D014469:Umbilical Arteries / Q000000981:diagnostic imaging