It does not replace them, because they are different types of test. In general terms, the Neo24 test is a screening test for patients with no previous abnormal findings related to their pregnancy. It is a non-invasive test, where neither the baby nor the placenta are sampled directly. In contrast, amniocentesis and chorionic villus sampling (CVS) are invasive, the former involves piercing the amniotic sac and removing a small sample of amniotic fluid containing foetal cells, while the latter removes cells from the placenta, which have associated risks for the pregnancy. The Neo24 test detects abnormalities in the number of chromosomes, not in their structure, whereas with amniocentesis and CVS a complete karyotype is obtained. Amniocentesis and CVS are used when a definitive result is necessary – for example, if an abnormality has been detected using a non-invasive test, or if abnormalities have been observed during an ultrasound examination. On the other hand, the Neo24 test can be performed from week 10, whereas for amniocentesis it is usual to wait until at least week 14 and CVS is not usually undertaken before week 11. In any case, your doctor will be able to explain which test is most appropriate in your case.