Prenatal diagnosis at 16 weeks of pregnancy can be performed using which of the following:

Amniocentesis is done during 16th week of pregnancy. Fetal blood sampling is done after 17-18 weeks, chorionic villi during 11-12 weeks of pregnancy, maternal blood AFP during 15-20 weeks. Ref: Textbook of Gynaecology By Dutta, 6th Edition, Page 108; In-Vitro Feilization By Kay Elder, Brian Dale, Yves Menezo, Joyce Harper, John Huntriss, 2010, Page 243; Donald School Textbook of Ultrasound in Obstetrics and Gynecology By Asim Kurjak, 2008, Page 755.