Maternal Serum Markers

Early in their pregnancy, all women are offered screening of several blood markers that can indicate increased fetal risk for certain genetic diseases and birth defects. Between 15 and 21 weeks’ gestation, a maternal serum sample is screened for alpha-fetoprotein (AFP), estriol and human chorionic gonadotropin (hCG). In addition, a fourth marker, inhibin-A, is included in some screenings.

AFP was the first protein marker to be associated with fetal abnormalities that was easily detectable in the mother’s blood. The fetus synthesizes high levels of AFP early in development, but the level in maternal serum is normally much lower. High concentrations of AFP in maternal serum are associated with open neural tube defects. During early development, the neural tube gives rise to the brain and spinal cord.