There are at least three very similar tests (Harmony, Panorama and Maternit21) that use a similar approach to look at circulating DNA from the placenta (which contains the baby's DNA) in the mother's blood. At ~11 weeks, there is usually enough circulating material to get a good sample. They screen for the three most common genetic trisomy conditions (13, 18 and 21), of which Down's Syndrome is the most common, and at least one of the tests also looks at duplications of the sex chromosomes (like Klinefelter's and Turner's syndrome). All can accurately determine the gender of the baby, but this is NOT the main reason they are performed.
It is worth asking your doctor. Some will only order the test if there is an increased risk of one of the genetic disorders due to advanced maternal age, family history or "soft markers" appearing on other scans. The testing is very accurate, but you will still be advised to have the even more definitive amnio or CVS to confirm a positive result (i.e. diagnosis of a problem).
I had the Maternit21 ('cause I'm old) at 12 weeks, and got results within ~10 days indicating normal chromosomes and a baby boy. For me, having the results provided some peace of mind, and there was no risk to the baby.
