Someone here please explain the difference between chorionic villus sampling and amniocentesis?

CVS and Amnio: A cvs is done earlier in pregnancy and involves getting tissue from the placenta. An amniocentesis is done later in pregnancy. It involves getting amniotic fluid from the gestational sac. Chromosomal abnormalities can be found by both techniques. An amniocentesis can also check for neural tube defects. A genetic disease, such as cystic fibrosis can be diagnosed by either technique.

Dr Brown and another doctor agreed

Placenta vs fluid: Cvs can usually be done earlier and involves obtaining placental tissue for chromosome analysis. This is done by needle biopsy either through the cervix or abdomen. Amniocentesis is obtaining amniotic fluid for testing also by needle aspiration. Both are done with ultrasound guidance, cvs slightly riskier with bleeding & cramping, both safe to do, both done by mfm docs. I hope that helps.