Firstly, the blood result is only about 10% of the overall score, so if you're unsure and the NT result was good, then maybe you don't need one. It's a personal decision. If you use an experienced practitioner, that lowers the risk.

How far along are you? I think the further along you are, the less the risk of m/c.

I had an amnio with DS2 at about 21wks. It hurt, but I breathed through it while DH held my hand. It was relatively quick and afterwards, they showed us baby's heartbeat. He was fine.

In our case, our baby later passed, but that wasn't related to the amnio. He had a serious illness. Which is why we had the amnio in the first place.