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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 -
First-trimester screening for trisomy 21 using nuchal translucency and nasal bone evaluations in a selected and an unselected population.
Sonek J, Cicero S, Nicolaides K.
Am J Obstet Gynecol 2007;196:19.