Prenatal diagnosis at 16 weeks of pregnancy can be performed using all of the following, except :

It is also called cordocentesis and involves per cutaneous cord blood sampling with a fine needle under ultrasound guidance.The common site is the umbilical vein at the placental cord inseion.It is usually done at or after 20 weeks. Chorionic villus sampling (CVS) is performed for prenatal diagnosis of genetic disorders. It is carried out transcervically between 10-12 weeks and transabdominally from 10 weeks to term. Amniocentesis (genetic) an invasive procedure, is performed between 14 and 16 weeks under ultrasonographic guidance. refer pgno:503 sheila textbook of obstetrics 2 nd edition. and Dutta,s Textbook of obstetrics page no 107 7th edition