The Combined Test is an examination of probability and does not permit you to recognize or exclude a chromosomal abnormality ith absolute certainty. If the risk is high, the fetus can be healthy, if the risk is low, the fetus may also be affected. The test works especially for some anomalies and chromosomal abnormalities, such as trisomy 21, 13, 18 and monosomy X. There are other more severe chromosomal abnormalities and rarer occurrence, which are not detectable by the combined test.