[Prenatal screening for Down's syndrome: a simplified method]

Prenatal screening for Down's syndrome (DS) can be achieved by combining maternal age risks and maternal serum additional parameters (AFP, HCG, uE3) by computer assisted statistical analysis. Nevertheless this measure of risk is far from broad and practical application in Italy, due to cultural and organization difficulties. So we suggest a different technical approach, the age specific risk being multiplied by the HCG/AFP likelihood ratio. HCG and AFP can be tested by an automated Elisa assay, and calculations performed by a simple method, excluding computer and software package use. About 100 pregnancies were evaluated both by a modified version of the Wald test and the method described hereafter. Using the automated HCG and AFP Elisa Testing and Crossley statistical calculation a higher False Positive Rate was observed. On the other hand no different Detection Rate was observed for the two tests. On a retrospective study we found that 5 sera from affected pregnancies were correctly identified both by the modified Wald test and the other method. It is concluded that, despite different False Positive Rates, the choice of which test to use depends on evaluation of local resources, one test being easier-to-perform and more sensitive, the other one probably being more specific but more difficult to perform.