Noninvasive Prenatal Screening For Fetal Aneuploidies And Microdeletions Using Cell-Free Fetal Dna

National guidelines recommend that all pregnant individuals be offered screening for fetal chromosomal abnormalities, most of which are aneuploidies, an abnormal number of chromosomes. Trisomy syndromes are aneuploidies involving 3 copies of 1 chromosome. Trisomies 21, 18, and 13 are the most common forms of fetal aneuploidy that survive to birth. There are numerous limitations to standard screening for these disorders using the maternal serum and fetal ultrasound. Noninvasive prenatal screening analyzing fetal cell-free DNA (cfDNA) in maternal serum is a potential complement or alternative to conventional serum screening. Noninvasive prenatal screening (NIPS) using cell-free fetal DNA has also been proposed to screen for microdeletions. Prenatal testing for twin zygosity using fetal cfDNA has been proposed to inform decisions about early surveillance for twin-twin transfusion syndrome and other monochorionic twin-related abnormalities.