Pregnancy-associated plasma protein A (PAPP-A), alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), and inhibin A, are biochemical markers that are part of the first and second trimester screening test, for Down syndrome and neural tube defects in pregnancy. These biochemical markers have been shown also to be associated with slightly increased risk for adverse pregnancy outcomes in the absence of aneuploidy or neural tube defects, for example; preeclampsia, low birth weight, placental abruption, preterm labor, and intrauterine fetal death.