Misscarriage

I had to faced misscarriage of my 7 weeks pregnancy.abrupt bleeding n pain while I was sleeping.doc told after an ultrasound that fetus sack was damaged n fetus ruptured.kindly plz any respected doctor guide me why this happened with me while my BP n sugar remains normal.n didn't have history of misscarriage.wanna ask how much chances to face same problem if I would conceive again?thanx in advance