However, many factors may affect NIPT results, such as placental chimerism, maternal obesity, and maternal cancer [22]. In general, FN results are likely caused by two factors. First, if the proportion of cffDNA does not meet a certain value, the positive signal may be indistinguishable from the background signal. Second, due to placental chimerism, the plasma cffDNA can be derived from an area of the placenta with either no chimerism or a low proportion of chimerism.