I agree with BabyBlue. If other tests (like the NT scan and blood work) suggest there's a higher than normal risk for down's, then an amnio is usually offered. But even then, it's totally up to her if she wants the test or not. The NT scan and blood work can give her an idea of her odds, but the blood test is also know for having false high odds for some women. And the amnio does carry a small risk of miscarriage. I'm 35 and I'm not having one done.
That's depends on the blood test.. if blood test show a woman has high risk DS.. then amnio will needed... usually it's for 35+ but sometimes under 35 still need it...
good luck