Pitfalls of prenatal diagnosis associated with mosaicism

Abstract

Fetal placental mosaicism, of which confined placental mosaicism is a subtype, occurs in 2–3% of pregnancies. Confined placental mosaicism may lead to a false positive result on non‐invasive prenatal testing (NIPT) for common aneuploidies. The risk of mosaicism in a chorionic villus sample (CVS) following a positive NIPT result is 2, 4, 22 and 59% for trisomy 21, 18, 13 and 45, X respectively. Following a positive NIPT result in the absence of a significant fetal structural anomaly (FSA), care is required in selecting the optimal diagnostic invasive test. Discussion of the limitations and implications is essential and referral to clinical genetics may be warranted.