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.