Z. Xu, MS, J. Xie, MD, PhD, J. Meng, MD, PhD, P. Li, PhD, X. Pan, MD, PhD, and Q. Zhou, PhD, “Non-Invasive Prenatal Diagnosis: A Comparison of Cell Free Fetal DNA (cffDNA) Based Screening and Fetal Nucleated Red Blood Cell (fnRBC) Initiated Testing”, N A J Med Sci, vol. 6, no. 4, Oct. 2013.