Snapshot A 41-year-old G3P1 presents to clinic 11 weeks pregnant. She has a history of 1 miscarriage and 1 uncomplicated live birth with no complications 10 years ago. Her daughter is healthy. She has no medical conditions. Vital signs are within normal limits. She receives first-trimester screening and a cell-free DNA test. Introduction Overview asseses if fetus has a genetic condition Epidemiology Incidence 1/150 live births with chromosomal abnormalities Risk factors advanced maternal age history of prior fetal aneuploidy or abnormality Pathogenesis Most from nondisjunction Some due to somatic mosaicism or translocations Studies First-trimester screening indications between 10-14 weeks gestational age serum labs serum free β-hCG or total hCG login to view 3 more bullets pregnancy-associated plasma protein A (PAPP-A) login to view 3 more bullets imaging ultrasound login to view 3 more bullets invasive studies chorionic villous sampling (sampling of prenatal villi) login to view 10 more bullets Second-trimester screening indications 15-22 weeks gestation (best time 16-18 weeks) serum labs quadruple screen login to view 12 more bullets invasive studies amniocentesis (sampling of amniotic fluid) login to view 7 more bullets Sequential integrated screening first trimester imaging login to view 2 more bullets serum labs login to view 1 more bullet second trimester serum labs login to view 1 more bullet higher detection rates than either first or second trimester screening alone Cell-free DNA indications to detect fetal Down syndrome 10 weeks to term pregnant patients at high risk for fetuses with Down syndrome highest detection rate for Down syndrome higher false-positive rate for low-risk patients