title: The thymic-thoracic ratio in fetal heart defects: a simple way to identify fetuses at high risk for microdeletion 22q11.
abstract: OBJECTIVE
  To establish reference ranges for the fetal thymic-thoracic ratio (TT-ratio) and to compare results with those from fetuses with congenital heart defects (CHD) with and without microdeletion 22q11 (del.22q11), a condition known to be associated with a hypoplastic thymus.
  
  
  METHODS
  TT-ratio was defined as the quotient of the anteroposterior thymic to the intrathoracic mediastinal diameters measured in the three vessels and trachea view. This ratio was measured in a prospective cross-sectional study of 302 normal healthy fetuses between 15 and 39 weeks' gestation. The study group comprised two groups: one group (CHDn) consisted of 90 fetuses with CHD and a normal karyotype with no del.22q11 and the other group (CHD(22)) included 20 fetuses with CHD and a normal karyotype but with proven del.22q11.
  
  
  RESULTS
  The TT-ratio of the normal fetuses did not show any statistically significant change during gestation, with a mean value of 0.44. The values of all 90 fetuses of the CHDn group were within the normal range and no different from normal fetuses. However, 19 of the 20 (95%) fetuses in the CHD(22) group had a significantly smaller TT-ratio (P < 0.001) compared with both the CHDn group and the normal fetuses, having a mean value of 0.25.
  
  
  CONCLUSIONS
  The TT-ratio is reliable and easy to obtain during fetal echocardiography. Fetuses with CHD and a low TT-ratio can be considered at high risk of having microdeletion del.22q11.
authors.affiliation: Center for Prenatal Diagnosis and Human Genetics, Berlin, Germany. chaoui@feindiagnostik.de
authors.forename: R
authors.initials: R
authors.lastname: Chaoui
authors.forename: K-S
authors.initials: KS
authors.lastname: Heling
authors.forename: A Sarut
authors.initials: AS
authors.lastname: Lopez
authors.forename: G
authors.initials: G
authors.lastname: Thiel
authors.forename: K
authors.initials: K
authors.lastname: Karl
mesh_terms: D002892:Chromosomes, Human, Pair 22 / Q000235:genetics*; D003430:Cross-Sectional Studies; D004452:Echocardiography; D005260:Female; D017353:Gene Deletion; D005819:Genetic Markers; D005865:Gestational Age; D006330:Heart Defects, Congenital / Q000000981:diagnostic imaging* / Q000235:genetics; D006801:Humans; D007621:Karyotyping; D011247:Pregnancy; D011446:Prospective Studies; D012016:Reference Values; D013950:Thymus Gland / Q000000981:diagnostic imaging*; D016216:Ultrasonography, Prenatal / Q000379:methods*
chemical_list: D005819:Genetic Markers