Ultrasound has an essential place in the performance of any invasive procedure and is important in avoiding damage to developing tissue. Chorionic villus sampling (CVS) is a prenatal test in which a sample of chorionic villi is removed from the placenta for testing. This chapter discusses in detail the invasive procedures in the first trimester of pregnancy. The most common indication for genetic amniocentesis is prenatal diagnosis. Amniotic fluid can also be used for biochemical determinations, enzyme study and deoxyribonucleic acid (DNA) hybridization. Use of color Doppler increases the success rate, as area of maximum color signal marks trophoblastic invasiveness and vitality.