It understands that childbirth is scary and dangerous, transformative and worthwhile.
In particular, I think it's false, to my own experience at least, to deny that there is something transformative about bringing children into this world. As a father, my son is just about the most important thing that's ever happened to me. I wouldn't say that he's made me "more beautiful, stronger, more sexual" than I'd ever been as a human (and I doubt my wife would say that he'd made her any of those things either)...but still. It's a pretty fucking big deal. Bella's transformation from human to vampire is in part a metaphor for her transition from woman to mother—a transition accomplished in fear, pain, terror, and love. And while I can't speak to that in terms of women changing to mothers, I can testify that, as a metaphor for the transition from man to father, it has a certain emotional veracity.