It depends if the doctor single or double stitched your uterus shut, also if your pushing your body too hard and too fast it'll re open. I had a single stitch on my uterus (not happy about it but I didn't think to tell the doc to double stitch me) and I was surgically glued shut on the outside, never re opened on me though.
Any incision can reopen once the staples or stitches are removed (or dissolve) if your incision didn't heal properly.