Confined Placental Mosaicism — Trisomy 16

A 32-year-old G2P1 woman undergoes routine chorionic villus sampling (CVS) at 11 weeks for advanced maternal age. The CVS karyotype returns **46,XX/47,XX,+16** (marked as **A** in the diagram) in 40% of cytotrophoblast cells. Follow-up amniocentesis at 16 weeks reveals a normal 46,XX karyotype in cultured amniocytes. Serial growth ultrasounds at 24, 28, and 32 weeks show progressive intrauterine growth restriction (IUGR) with abdominal circumference falling from the 25th to the <3rd centile. Umbilical artery Doppler shows elevated S/D ratio but maintained end-diastolic flow. Which of the following BEST describes the clinical significance of the karyotype abnormality marked **A**?