Basically it gets your brain to focus on the facts which is very calming. Some of the facts I find helpful are “miscarriage is unlikely statistically to happen to me again” “I am safe right here and right now” etc.
Congratulations! And yes this type of anxiety isn't good for you. At 10w I bought a doppler for reassurance that helped me a lot. Takes time to pick up the heartbeat for initial couple of weeks as the fetus is too small. So don't panic if you don't hear. But I highly recommend it from my experience.
You’re not alone. Ugh. So I’ve learned a lot of techniques from therapy. I practices DBT therapy and there’s this thing called “wise mind” which really helps when I’m drowning in sadness or anxiety