A screening test checks the chances of the fetus having a certain disease. When screening test results are positive, it means that the fetus has a higher chance of having the disease, but this is not confirmed.
Confirmation is via a diagnostic test. Why not do a diagnostic test right the from start then?
This is because diagnostic test are usually more expensive, or more difficult to perform and often carry a higher risk.
A screening test should be:
- Widely available
- Non invasive
- there must be a diagnostic test for follow up