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Maternal plasma cell-free fetal and maternal DNA at 11-13 weeks' gestation: relation to fetal and maternal characteristics and pregnancy outcomes.
Poon LC, Musci T, Song K, Syngelaki A, Nicolaides KH.
Fetal Diagn Ther 2013;33:215-23. pdf -
Cell-free DNA levels in pregnancies at risk of sickle-cell disease and significant ethnic variation.
Gerovassili A, Nicolaides KH, Thein SL, Rees DC.
Br J Haematol 2006;135:738-41.