This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Gynaecology & Obstetrics
A women undergoes a chorionic villous sampling at 11 weeks gestation. The result shows two cell lines - 46 xy and 47 xy + 21 what is your next step 
Select and explain. 
A. Repeat CVS at 13 weeks gestation, B. No need to evaluate further, C. Do amniocentesis for further confirmation, D. Diagnose as Down syndrome and counsel the couple
C: Do amniocentesis for further confirmation
Answer: C: Do amniocentesis for further confirmation 
Explanation: This is a case of mosaicism. In most cases, the mosaicism reflects confined placental mosaicism rather than true second cell line within fetus.
Amniocentesis should be offered, and if results are normal, mosaicism is presumed to be confined to placenta.
Confined placental mosaicism can cause IUGR and stillbirth.