Both are invasive prenatal diagnostic techniques. The gynecologist should be the one to indicate when to perform one or the other depending on the gestational age.
The earliest is a chorion biopsy, which can be performed between the 10th and 14th week of pregnancy. The risk of miscarriage is 7-8%. It is performed by removing a small sample of chorionic villi.
Amniocentesis can be done between 16-18 weeks of pregnancy. It is performed by extracting amniotic fluid. The risk of miscarriage with this technique is 0.6 and 1%.
Both present a risk of natural termination of pregnancy.