You mean the triple testing when your pregnant for downs etc? If so its quite common if not necessary actually not sure if it is necessary but not something I would refuse anyway. If the test results were high chanced the test that follows can cause complications and spontanous abortion of baby sadly

We decided should that happen to us that we would not get the followup test and that we would just be prepared mentally that baby may have been born with downs.
Sorry if I've confused what you mean x