These are various terminologies roughly denoting the same aspect of fetal evaluation. Firstly we need to understand what is Down Syndrome and why some parents may prefer to screen for it during pregnancy.
Screening test means a test that will tell you if you have or don’t have, a higher than average chance of having that condition. It is NOT a diagnostic test – meaning, it cannot say if that condition is truly present.
Down syndrome screening test carried out in the first three months of pregnancy is currently the standard test for this condition. It is a combination of measuring the baby’s neck-fluid thickness (“nuchal”) and certain hormones produced by the baby’s placenta (hCG and PAPP-A). Hence this test is called combined screening test. Since the nuchal translucency (neck fluid thickness) is the most important component of this test, it also sometimes (though a bit less accurately) referred to as nuchal test.