This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General obstetrics, Subject name: Anatomy
Karyotyping of fetus can be done through all the following invasive methods except: 
Select and explain. 
A. Amniocentesis, B. Cordocentesis, C. Chorionic villi sampling, D. Fetal skin biopsy
D: Fetal skin biopsy
Answer: D: Fetal skin biopsy 
Explanation: Fetal karyotyping can be done by Chorionic villi sampling Cordocentesis Amniocentesis Fetal skin biopsy is done to detect any chromosomal anomaly. It is done between 17-20 weeks to detect serious skin disorders like epidermolysis bullosa,oculocutaneous albinism. Ref: Williams Obs 23e pg 299-301.