Is there a blood test to see if you're a carrier for downs syndrome?

Yes: Since almost all cases of Down syndrome (maybe 95-98% of cases) are not inherited from carrier parents, the testing of the parents' chromosomes is probably not done unless a Down syndrome baby has been born, and the chromosomes of the baby suggest that one of the parents may be a carrier.

Yes: The features of Down syndrome can be passed by a carrier (someone with a piece of a 21 chm in a balanced swap with another chm).The egg/sperm of that individual may pass extra 21 material & conceive a ' translocation down syn ' which makes up <2% of ds. Ds is not carried like sickle cell or cystic fibrosis inbedded in genes.If your chms are nl your risk is that of the population & more age related.