Ah, bunnys mama -
That surely is a sad question ... I've only attended about 300 births, and in that time, only 2 were stillborn (that is, right before they were supposed to be born) - one of them my own. I couldn't tell you the "national statistic", but truly I believe that most of us get here just fine.
Causes?? Of those two, no one could give any physical explanation at all as to why that happened. Sometimes, there are obvious reasons - like the baby had severe problems and just couldn't make it to birth. (Oh, a side point, only 3% of ALL pregnancies have birth defects.)Or the mom had health concerns that just wouldn't let a healthy baby develop.
For myself, I believe that my son didn't need to be born into this life, into that body. He taught me some powerful lessons about trust and letting go, and although I can't say I know this, he's with us now as our second child. And that's the most hopeful thing I can think of when there are unexplained/unexplainable stillbirths; that their lives served some purpose even though we didn't get to know them as they grew up.
The bridge between life and death is so thin at the moment of birth - but here we are!
If you are worried or in pain over this subject, I wish you peace and hope for the future
mama to Jacob, 10/23/98, Noah, 10/25/99 and EDD of ??/4/02