I've heard different thing's that the egg will always attach after its fertalized. Then other times I've heard that it's a 50/50 chance it will and stay attached if not it will flsh out with our menstrual cycle.then I've heard stress will cause the embryo to unattached. I'm 14 but I'm interested in this kind of thing. I'm not saying I'm going to get pregnant now but when I'm married notstill in school or collage. Thank you to anyone that answer's. :)

Oh girl! There are many reasons it doesn't attach. In nursing school this was a whole weeks lecture with a test at the end.

It may be a hostile uterus, the egg was not completely fertilized, infection... oh there are more reasons than I have fingers on my hands!