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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 -
Screening at 11-13+6 weeks' gestation.
Sonek JD, Nicolaides KH, Janku P.
Ceska Gynekol 2012;77:92-104.