PAPPA and Down syndrome: Associations between first- and second-trimester serum markers and adverse pregnancy outcomes among those who underwent prenatal screening for Down syndrome in our clinic were studied. The adverse pregnancy outcomes, serum levels of pregnancy-associated plasma protein-A (PAPP-A), β-human chorionic gonadotropin (β-hCG), and maternal serum alpha-fetoprotein (ms-AFP) were recorded and analyzed.