It'a already possible to test for trisomy in a fetus. There's a newish method (NIPT) that does analysis on maternal blood which has very low risk (it's named non-invasive, but drawing blood is routine but not risk free). Having a treatment, if it's feasible, might be more (or less) paletable than ending the pregnancy when diagnostics indicate likely trisomy.

NIPT is non-invasive compared to amniocentesis