Chorionic Villous Sampling Introduction sampling of placental villi as a means of prenatal genetic testing based on assumption that the placenta has the same genetic makeup as the developing fetus can be performed at 10-12 weeks can follow up an abnormal first trimester screen following confirmatory ultrasound Complications transverse limb abnormality risk greatest when performed < 10 weeks rupture of membranes chorioamnionitis Amniocentesis Introduction sampling of amniotic fluid as a means of prenatal genetic testing based on capture of free-floating fetal cells in the amniotic fluid also used to drain amniotic fluid in setting of polyhydramnios and sample fluid when chorioamnionitis suspected can be performed 14-18 weeks used to follow-up an abnormal quad screen can only be considered after an ultrasound confirms gestational age, single and viable intrauterine pregnancy, and the absence of fetal abnormalities that might explain the abnormal quad screen Complications rupture of membranes chorioamnionitis