The blood test/nuchal scan pick up a lot more than just Downs, the same "soft markers" can indicate other trisomy problems such as turners or Edwards, or heart problems.
The diagnostic tests will tell you what the problem is, but with some risk.
You should bear in mind that if a baby has one of these problems, it is MUCH more likely to miscarry or be stillborn. Even with Downs, which has a higher degree of "survivability" than the other trisomies, something like three-quarters of affected babies will miscary usually in the first 4 months, be stillborn or die in the first week after birth.
With turners and Edwards babies, more than 90% are lost early, or die soon after birth.
I'd rather know. even if you are against termination, you can prepare for the possibility losing the pregnacy, and in the case of heart problems, the sooner the diagnosis is made, the sooner they can prepare to operate (sometimes even in the womb).
I have every blood test offered (there's no reason not too, it's putting knowlage in your hands, it's not forcing you to do anything further).
I have also had CVS recently, due to high risk (all was fine).