Can do a blood test on the mother for Down's. Enough baby DNA leaks out into her bloodstream and you can see if the chromosome ratios are the slightest bit off or not.

i wonder does the mother get any phenotype if she has a lot of dna in her bloodstream that has too many chromosomes

Same here, for our second child, since her mother had moved into a higher-risk age category by then. This was in San Francisco in 2005.