Late term abortion

I know its a sensitive subject, but for all of the mothers who've lived through a natural late term abortion (30 weeks +) were there any signs or what was the reason for your child's passing?

I've always been told once you're past 27 weeks you're in the clear unless something goes wrong during labor and your baby stops breathing.

Now I'm seeing a lot of ultrasound pictures as far as 37 weeks where mothers are saying they lost their child (before labor).

I'm curious to know the things that could cause this or if sometimes there's no reason at all.