title: Assessment of the fetal thymus by two- and three-dimensional ultrasound during normal human gestation and in fetuses with congenital heart defects.
abstract: OBJECTIVE
  Our objectives were to compare the size and volume of the developing fetal thymus obtained by two-dimensional ultrasound (2D-US) and three-dimensional ultrasound (3D-US), develop normative data for thymus volume (TV), and investigate TV in fetuses with congenital heart disease (CHD) and normal twin gestations.
  
  
  METHODS
  We studied 321 fetuses (gestational age (GA): 17-39 weeks) including 238 normal singletons, 64 normal twins and 19 singleton fetuses with CHD. We used 2D-US to assess fetal thymus maximum transverse diameter (MTD), maximum transverse area (MTA), anteroposterior diameter (APD) and superoinferior diameter (SID). TV was obtained by 3D-US using virtual organ computer-aided analysis. Measurements were adjusted for estimated fetal weight where appropriate. Linear regression analysis, general linear models and Fisher's Z-transformation were used where appropriate. A nomogram of fetal TV based on singleton gestations was produced according to previously published methods.
  
  
  RESULTS
  Ultrasound assessment of the fetal thymus was possible in 95.3% (306/321) of cases. Both 3D-US and 2D-US measurements were significantly correlated with GA (TV r = 0.989; MTA r = 0.918; MTD r = 0.884; APD r = 0.849; and SID r = 0.816; all P < 0.05). After Fisher's Z-transformation, the correlation between the TV and GA was significantly stronger than that between any individual 2D-US measurement and GA (P < 0.05). Normal twin fetuses had TVs similar to those of singletons adjusted for estimated fetal weight and GA (P = 0.85). TV adjusted for estimated fetal weight and GA was significantly lower in fetuses with CHD than in normal singletons (P < 0.05).
  
  
  CONCLUSIONS
  2D-US and 3D-US are useful tools for evaluation of the size and volume of the human fetal thymus through gestation. Fetal TV by 3D-US seems to reflect normal development of the thymus in utero better than do 2D-US measurements. Lower TV should be expected in association with CHDs.
authors.affiliation: Department of Ultrasonic Medicine, The Second Xiangya Hospital, Central South University, Changsha, Hunan, P R China.
authors.forename: L
authors.initials: L
authors.lastname: Li
authors.forename: M O
authors.initials: MO
authors.lastname: Bahtiyar
authors.forename: C S
authors.initials: CS
authors.lastname: Buhimschi
authors.forename: L
authors.initials: L
authors.lastname: Zou
authors.forename: Q-C
authors.initials: QC
authors.lastname: Zhou
authors.forename: J A
authors.initials: JA
authors.lastname: Copel
mesh_terms: D004200:Diseases in Twins / Q000000981:diagnostic imaging / Q000473:pathology; D019560:Echocardiography, Three-Dimensional; D005260:Female; D005318:Fetal Heart / Q000000981:diagnostic imaging / Q000196:embryology; D005865:Gestational Age; D006330:Heart Defects, Congenital / Q000000981:diagnostic imaging* / Q000473:pathology; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D009929:Organ Size; D011247:Pregnancy; D013950:Thymus Gland / Q000000981:diagnostic imaging* / Q000196:embryology; D016216:Ultrasonography, Prenatal