Final answer:
Maternal serum concentrations of hCG and alpha-fetoprotein rise during a normal pregnancy, while estrogen levels continuously increase. Progesterone levels increase for the most part but may decrease late in pregnancy to permit labor contractions.
Step-by-step explanation:
The question concerns the changes in maternal serum concentrations during normal pregnancy. Throughout pregnancy, levels of certain hormones increase, while others maintain or decrease later in gestation. Specifically, human Chorionic Gonadotropin (hCG) is produced by the placenta after implantation.
This hormone's levels rise during the early stages of pregnancy. Alpha-fetoprotein (AFP) also increases during pregnancy and is sometimes used as part of prenatal screening tests. Progesterone levels, which inhibit uterine contractions and support pregnancy maintenance, increase during most of the pregnancy but may decrease near the end to allow uterine contractions for labor. Estrogen levels continuously rise throughout pregnancy to maintain it and promote fetal and maternal tissue growth.