I've always had horrible cramps, heavy periods and had surgery for endometriosis twice. I was actually on my way in for a pre-op physical for the third surgery when we found out about baby number 4.
I have had easy labors and deliveries. Actually my 4th baby (born in May) was the most difficult yet. Just a really big baby, my back was bad, getting older, and the baby before that was only 14mo old when I got Pg again!
I've never, ever, heard that correlation before.