TY - JOUR AU - Kagan, K O; Wright, D; Nicolaides, K H TI - 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 JO - Ultrasound Obstet Gynecol VL - 45 PY - 2015 DO - 10.1002/uog.14691 SP - 42 EP - 47 ER -