Advantages of the single nucleotide polymorphism- based noninvasive prenatal test

the placenta into the maternal circulation as the cells break down (apoptosis) and the DNA becomes fragmented [4,5]. Circulating fetal cfDNA comprises approximately 3-13% of the total maternal cfDNA. These DNA fragments can be detected as early as 4 weeks of gestation and are generally cleared out within 2 hours after childbirth [6-8]. A noninvasive prenatal test (NIPT) using cfDNA has proven to be highly sensitive and specific for detecting trisomy 21 in both highand low-risk groups [1,2,9,10]. At present, there are about five major companies providing commercial NIPT services globally (Fig. 1). NIPT using cfDNA is now available through these providers in more than 60 countries. According to business reports, over 500,000 NIPT studies on women with a high risk for fetal aneuploidy were performed in the United States in 2013 [11]. These companies have published several articles showing that their own method is very effective for screening for trisomy 21, 18, and 13 Advantages of the single nucleotide polymorphismbased noninvasive prenatal test