3% chance of miscarriage??

I had my first ultrasound with my OB at my fertility specialist's office today. She said at our next u/s next week (I'll be almost 7w) that once we hear the heartbeat, chance of miscarriage drops to 3%. 
Is this real? I thought that miscarriage risk stays high throughout the first trimester. I am trying to figure out when we should announce- I was originally thinking about 10w. But now that she said this I am thinking 8w...I'm torn. This is our first pregnancy after trying for literally years. 
What do you think?