Normal range: Risk factor is calculated on an individual basis, related to LMP, weight and date of birth
Comment: AFP/HCG test (dual screen) is used to help predict the risk of certain birth detects about 55% of Down syndrome cases, while classifying 5% of normal patients as abnormal. Further addition of Estriol increases detection to 60% and false positive rate to 7%
Sample: Serum, LMP, age, weight, birth date, number of embryos, smoker