 This can be done at 10–12 weeks gestation by a procedure called chorionic villus sampling (CVS) that involves removing a tiny piece of the placenta and analyzing DNA from its cells.It can also be done by amniocentesis after 14 weeks gestation by removing a small amount of the amniotic fluid surrounding the baby and analyzing the cells in the fluid.Each of these procedures has a small risk of miscarriage associated with it and those who are interested in learning more should check with their doctor or genetic counselor.