Small thymus and Thymic-Thoracic Ratio in fetuses with trisomy 21

Purpose: An absent or hypoplastic thymus is known to be a typical sign in fetuses with deletion 22q11 (DiGeorge-Syndrome). A small thymus, reflected by a small Thymic-Thoracic Ratio (TT-Ratio), was recently described to be found in fetuses with trisomy 21. This study aimed to confirm this observation on data of 2nd and 3 rd trimester fetuses with trisomy 21. Material and methods: Fetuses undergoing invasive procedure for being at high risk for aneuploidy or with cardiac defects had a comprehensive fetal echocardiography. The TT-Ratio was measured as described before. The ratio measured in fetuses with Down's syn…