-
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 -
Prospective validation of first-trimester combined screening for trisomy 21.
Kagan KO, Etchegaray A, Zhou Y, Wright D, Nicolaides KH.
Ultrasound Obstet Gynecol 2009;34:14-8.