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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 -
Dose dependency between cigarette consumption and reduced maternal serum PAPP-A levels at 11-13(+6) weeks of gestation.
Kagan KO, Frisova V, Nicolaides KH, Spencer K.
Prenat Diagn 2007;27:849-53.