Blood test regarding healthy baby?

doeie04

SIL is insisting I go get a blood test to make sure baby is healthy.

Backstory: She had two losses while in the first trimester before having a healthy baby boy. She wants us to get a blood test to make sure baby is healthy, and to ease her mind. (Which I totally understand her worry.) We aren't very close, so this is even more weird to me. She didn't even ask me how I was feeling until last week (she has known for 6 weeks) and then proceeded to tell me I needed to get testing done. 

I have a few questions. I thought after the first few weeks of finding out, the blood tests don't really tell much. I know you can go in and see if you are doubling, but if I go in they are going to give me a hCg level and it won't mean anything, unless it is really low, since every pregnancy progresses differently, right?

What would the point of getting a blood test tell me at this point in our pregnancy, besides that I am pregnant, which I already know?

We haven't had an ultrasound done. We were waiting until 20 weeks. We will be meeting with our MW in two weeks to hear the heartbeat, which I have already heard on our doppler, which is why we felt comfortable telling everyone. I am looking into an earlier ultrasound just to ease my mind of a missed miscarriage and twins.