Prenatal diagnosis
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Noninvasive prenatal diagnosis of fetal Down syndrome using direct nucleic acid analysis was once an elusive goal. The presence of cell-free fetal DNA in maternal plasma was discovered in 1997 and offered a new noninvasive source of fetal genetic material. ⋯ A number of multicenter studies have since been conducted to evaluate the diagnostic efficacy of the sequencing-based method. To date, the literature contains results for the analysis of a total of 305 trisomy 21 pregnancies and 2061 euploid pregnancies. The overall diagnostic sensitivity and specificity were both 99%. Besides trisomy 21, massively parallel maternal plasma DNA sequencing has also been applied to the noninvasive detection of trisomy 18, trisomy 13 and fetal genetic sequences across the genome.