Chance of miscarrying?

I have no reason to believe I will ever miscarry but just for assurance what's the chance?? im 13 weeks. I've had absolutely no bleeding since the last time I had a period. Blood work showed the baby has always been exactly where it should be. (regarding hcg levels) they've always measured exactly on time. They had a strong heart rate of 172. I eat pretty healthy, take prenatals (since week 5) drink lots of water and don't have anything in my life that causes strenuous activity. I also stay at home at all times expect for shopping, although I still get excerise from housework and grocery shopping. I've also cut out caffiene almost entirely except for occasions where I'll have a glass. I've also never miscarried in the past. We're hoping for the best but I can't help but worry. What's the chance?