I think the chance of miscarriage is 50% in the first 4 weeks. Then it goes down ALOT. Doctors aren't very reassuring about this stuff but I'm 18 and my baby is perfectly healthy (as far as I know.) I've also never had a miscarriage even though my mum had 3.
There is no reason why being 18 would make you any less capable of carrying a baby without miscarriage. 13 year olds do it, and do it well. I'm sure you'll be fine
