I had it with all three of mine, but only did the blood screening on top of the NT scan with my third. He came back 1 in 34, cue panic as I also wouldn't terminate. I refused invasive testing and spent 20 weeks worrying and researching myself stupid, before finally having a late amnio at 32 weeks. The only risks then are of premature labour, which are the same, 1 in 100 or so, as pregnancy loss at the earlier gestation. DS had typical chromosomes and so I could at least spend a few weeks not worrying! If we had heard differently I would have had time to prepare emotionally not to mention do even more research.
However that nightmare was three years ago. Something anyone facing this decision should now know if you don't already is that there is a very very NEW non-invasive blood test only recently available in the UK that gives you a 99% result from as early as 10 weeks. Essentially if the test is negative, baby is pretty much not likely to not have Down Syndrome. If the test is positive, baby is 90-99% likely (depending on the stats you read), so you can decide what to do from there. It's called Harmony (there's an equivalent called MaterniT21 in the US) and boy do I wish it was around a few years earlier. It's not cheap, but I would have paid that for peace of mind. It will probably roll out to the NHS eventually, but not any time soon.
The regular blood screenings can also reveal non-genetic issues - for instance I had low PAPP-A (this was the main cause of the screen positive) which, for some women, can mean issues with the placenta later on, and it meant I got an extra scan for growth. DS was fine, but he could so easily not have been as happened to a friend who also had low PAPP-A, later growth restriction and a necessarily early delivery of a now very healthy little boy.
It's all a hugely personal decision, but I firmly believe before making that decision that people should be aware that there may be more choices they didn't know about and that the standard NHS blood test has uses beyond screening for DS.