Natera Panorama Practice Exam

In this counting method, the test looks at how many DNA fragments from each chromosome are present in maternal blood to infer fetal chromosomal status. If a twin vanishes early, its fetal DNA can linger in the maternal plasma for a while. That residual DNA can skew the chromosome counts, creating signals that look like aneuploidies or unusual sex chromosome patterns. As a result, the test can produce false positives and may give an incorrect fetal sex call because the counted DNA reflects both the live fetus and the vanished twin rather than just the current fetus. This is a recognized pitfall in NIPT with the counting approach.