The quad screen measures high and low levels of AFP, abnormal levels of hCG and estriol, and high levels of Inhibin-A. The results are combined with the mother's age and ethnicity in order to assess probabilities of potential genetic disorders.
High levels of AFP may suggest that the developing baby has a neural tube defect such as spina bifida or anencephaly. However, the most common reason for elevated AFP levels is inaccurate dating of the pregnancy.
Low levels of AFP and abnormal levels of hCG and estriol may indicate that the developing baby has Trisomy 21(Down syndrome), Trisomy 18 (Edwards Syndrome) or another type of chromosome abnormality.