Worried miscarriage will happen to me too?

I currently am 7 weeks pregnant, and I go for my first prenatal appointment at 8 weeks. My best friend was pregnant also, supposed to be 13 weeks. She went in yesterday to hear the heart over the doppler and they could not find it. They did an ultrasound and there ended up being no heartbeat. Her baby measured only 10 weeks, so she must have lost it then. She is scheduled to have a D&C after the weekend. I was wondering how often does something like this happen to people?