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Integrated ultrasound and biochemical screening for trisomy 21 using fetal nuchal translucency, absent fetal nasal bone, free beta-hCG and PAPP-A at 11 to 14 weeks.
Cicero S, Bindra R, Rembouskos G, Spencer K, Nicolaides KH.
Prenat Diagn 2003;23:306-10.