Losing your baby after 1st trimester

I see lots of posts of parents who lost their babies at a late stage in pregnancy like between 20-30 weeks pregnant. I can’t even imagine how hard that is since i had a miscarriage at 6 weeks before, but i was wondering what causes someone to lose a baby that far along!?

I am 6 weeks pregnant now and really worried that anything can happen..

I just would like to know what might cause a baby to not make it in 2nd or 3rd trimester.

And to all moms who did lose a baby at any stage , you are very strong!