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First-trimester contingent screening for trisomy 21 by biomarkers and maternal blood cell-free DNA testing.
Nicolaides KH, Wright D, Poon LC, Syngelaki A, Gil MM.
Ultrasound Obstet Gynecol 2013;42:41-50. pdf -
Placental expression of alpha and beta subunits of human chorionic gonadotrophin in early pregnancies with Down's syndrome.
Brizot ML, Jauniaux E, Mckie AT, Farzaneh F, Nicolaides KH.
Hum Reprod 1995;10:2506-9.