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
[{'content': 'Karyotyping of fetus can be done through all the following invasive methods except: \nSelect and explain. \nA. Amniocentesis, B. Cordocentesis, C. Chorionic villi sampling, D. Fetal skin biopsy', 'role': 'user'}, {'content': 'Answer: D \nExplanation: 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.', 'role': 'assistant'}]