hCG: human chorionic gonadotropin
NB: nasal bone
NT: nuchal translucency
PAPP-A: pregnancy-associated plasma protein-A
A prenatal screening test combining free Beta-hCG, PAPP-A, NT and NB. It is a proven and prospectively validated technology in over 200,000 pregnant women. It is used in the first trimester of pregnancy to determine the risk of Down syndrome with a very high sensitivity and specificity.
A screening procedure in which both first and second trimester screening are performed. However, the first trimester screening results are not provided to the physician and patient but are withheld until after the results of second trimester screening are available, late in pregnancy. Physicians should also be aware that many laboratories offering this protocol are using a Down syndrome risk cut-off of 1 in 100. As a result, patients at moderately increased risk will not be offered the option of amniocentesis with this protocol. Further, physicians should be aware that 20-30% of patients will not undergo first or second trimester screening steps and could have no final Down syndrome screening results. Since the patient needs to have two different blood draws, the cost is higher for the patient.
A second trimester test consisting of AFP, total hCG, inhibin A and unconjugated Estriol (uE). The test can detect about 70% of Down syndrome cases with an expected false positive rate of 5%. Some studies have observed a false positive rate significantly higher than 5%.
Triple Serum Screen
Triple test that includes only AFP, total hCG and unconjugated Estriol (uE), has a higher false positive rate when compared with the Quad test.