Maternal mosaicism for a large segmental duplication of 18q as a secondary finding following non-invasive prenatal testing and implications for test accuracy

What's already known about this topic? Non‐invasive prenatal testing (NIPT) of cell‐free DNA from maternal plasma is a sensitive method of identifying pregnancies at risk of trisomies 21, 18 and 13. This technology analyses both maternal and fetal cell‐free DNA in the maternal plasma. Abnormal NIPT results should be confirmed with invasive testing. What does this study add? Structural imbalances of fetal chromosomes may be identified occasionally during NIPT. Maternal mosaicism for an unbalanced structural chromosomal rearrangement may be a rare cause of increased risk NIPT results.