First trimester Down syndrome screening with dried blood spots using a dual analyte free beta hCG and PAPP-A immunofluorometric assay.

OBJECTIVE: To determine the effectiveness of first trimester Down syndrome screening with dried blood spots using a dual analyte free beta human chorionic gonadotrophin (hCG)/pregnancy-associated plasma protein A (PAPP-A) immunofluorometric assay.
METHOD: An initial retrospective study of 54 Down syndrome cases and 1064 control specimens was performed followed by a series of 146,513 specimens from routine screening. Detection rates at a fixed 5% false-positive rate were determined separately based on reference data from the retrospective study set and then adjusted based on the routine screening study set.
RESULTS: On the basis of the retrospective analysis, the estimated detection rate using free beta hCG, PAPP-A and maternal age varied from 78% at 9 weeks of pregnancy to 70% at 13 weeks of pregnancy. Using a combined protocol, including NT, the detection rate varied from 92 to 90% between 9 and 13 weeks of gestation. Adjusting distribution parameters based on the routine screening dataset reduced the detection rate by at most 1%.
CONCLUSION: Analysis of free beta hCG and PAPP-A using a dual analyte dried blood spot assay is an effective tool in Down syndrome screening, adding an important option for those considering implementation or modification of existing prenatal screening programs.