Chorionic Villous Sampling Introduction sampling of chorionic villi for prenatal genetic testing or screening based on the assumption that the placenta has the same genetic makeup as the developing fetus Procedure under ultrasound guideance, transcervical or transabdominal sampling of chorionic villi tissue is performed Indications typically done at 10-12 weeks gestation, following abnormal first-trimester screening diagnostic testing of choice prior to 15 weeks of gestation karyotyping Complications pregnancy loss rate is 1-2% transverse limb abnormality risk greatest when the test is performed at < 10 weeks gestation rupture of membranes chorioamnionitis Amniocentesis Introduction sampling of amniotic fluid for prenatal genetic testing or screening detection of free-floating fetal cells in the amniotic fluid Procedure under ultrasound guidance, amniotic fluid is extracted via transabdominal needle insertion Indications typically done at 14-18 weeks gestation, after abnormal second trimester screening diagnostic testing of choice after 15 weeks gestation karyotyping diagnosis of chorioamnionitis, fetal lung maturity (lecithin-sphingomyelin ratio), and Rh incompatibility treatment for polyhydramnios Complications pregnancy loss rate is 0.5-1.0% rupture of membranes chorioamnionitis