see Fetoplacental mosaicism: potential implications for false-positive and false-negative noninvasive prenatal screening results
A recent retrospective study of nearly 53,000 prenatal tests for common fetal chromosomal abnormalities un-derscores the need for clarity when offering noninvasive prenatal screening (NIPS) to pregnant women. Grati et al. found that fetoplacental mosaicism, in which placental and fetal cells differ in containing aneuploid cells, can result in small but measurable rates of both false-positive and false-negative findings. The study, which ana-lyzed the results from a large database of prenatal testing cases in which NIPS results were confirmed by direct testing of placental and fetal DNA, showed that for the common trisomies (13, 18, and 21) false-positives can be expected in 1 in 3,006 cases and false-negatives can be expected in 1 in 107. The potential for false results led the authors to suggest that those offering NIPS counsel patients that the tissue being sampled is of placental origin and thus may not perfectly reflect the status of the fetus. To ensure that patients understand the implica-tions of fetal-placental mosaicism, the authors propose that the term "cell-free fetal DNA" be changed to "cell-free placental DNA." The change in terminology should help providers inform patients of the test's limitations and the potential need for confirmatory invasive testing. —Karyn Hede, News Editor
