Antenatal diagnosis of Down syndrome: how good is state of the art.

A newborn with Down syndrome can be expected once in a thousand deliveries. Amniocentesis for karyotyping of foetal cells or detection of foetal cell in the maternal circulation ie, fluorescent in-situ hybridisation (FISH) and karyotyping, are definitive methods of making the diagnosis antenatally. The cost of doing this routinely in all pregnancies is prohibitive. This has led to dependence on screening tests, to select women more likely to be carrying a Down foetus, to offer karyotyping in a more cost efficient manner. Unfortunately, these screening criteria, namely maternal age, biochemical markers and ultrasound pointers, are rather insensitive and miss a large number of cases of Down syndrome. At the same time they are very non-specific, picking up a large number of false positive cases, resulting in undue anxiety and unnecessary alarm in a large number of mothers. Till a non-invasive, definitive test, like FISH can be routinely used in all pregnancies at affordable costs, accurate antenatal diagnosis on a community basis will be a hit and miss affair.