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First-trimester contingent screening for trisomy 21 by biomarkers and maternal blood cell-free DNA testing.
Nicolaides KH, Wright D, Poon LC, Syngelaki A, Gil MM.
Ultrasound Obstet Gynecol 2013;42:41-50. pdf -
Detection of trisomy 21 by quantitative mass spectrometric analysis of single-nucleotide polymorphisms.
Tsui NB, Chiu RW, Ding C, El-Sheikhah A, Leung TN, Lau TK, Nicolaides KH, Lo YM.
Clin Chem 2005;51:2358-62.