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Analysis of Cell-Free DNA in Maternal Blood in Screening For Aneuploidies: Updated Meta-Analysis.
Gil MM, Accurti V, Santacruz B, Plana MN, Nicolaides KH.
Ultrasound Obstet Gynecol 2017;50:302-314. pdf -
Screening for trisomy 18 by fetal nuchal translucency and maternal serum free beta -hCG and PAPP-A at 10-14 weeks of gestation.
Tul N, Spencer K, Noble P, Chan C, Nicolaides K.
Prenat Diagn 1999;19:1035-42.