 Thus for even greater accuracy of predicting risks, the outcome of the nuchal scan may be combined with the results of simultaneous maternal blood tests.In pregnancies affected by Down syndrome there is a tendency for the levels of human chorionic gonadotropin (hCG) to be increased and pregnancy-associated plasma protein A (PAPP-A) to be decreased.The advantage of nuchal scanning over the previous use of just biochemical blood profiling is mainly the reduction in false positive rates.