Its not about haveing a baby. There are two versions of this song. If you know anything about Flyleaf you would have realized there are almost allways two versions of a song. So both lyrics are right.
"of my own heart making your blood flow so that your chest can rise and fall" "of my own heart griveing in your hands you crush me when you run that way" and "In the shadows you 'slept fine', or 'shant find' and when will you whisper to me so you can rest" so you see both lyrics are correct depending on which version of the song you have.