Why could a woman have three Trisomy 21 pregnancies? – a case report

Key Clinical Message Mosaicism, an important cause for recurrent T21, should be suspected in families with more than one affected child wishing to receive prenatal counseling. Fluorescence in-situ hybridization analysis in a large number of cells and in different tissue samples is critical for detecting low-level mosaicism and is a key prognostic factor.