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First-trimester contingent screening for trisomies 21, 18 and 13 by fetal nuchal translucency and ductus venosus flow and maternal blood cell-free DNA testing.
Kagan KO, Wright D, Nicolaides KH.
Ultrasound Obstet Gynecol 2015;45:42-7. pdf -
A screening program for trisomy 21 at 10-14 weeks using fetal nuchal translucency, maternal serum free beta-human chorionic gonadotropin and pregnancy-associated plasma protein-A.
Spencer K, Souter V, Tul N, Snijders R, Nicolaides KH.
Ultrasound Obstet Gynecol 1999;13:231-7.