Starting labor..?

I am going to be a second time mom in around 16-18 days. When I was pregnant with my daughter she was a little over 2 weeks over due. I keep reading posts, comments and articles about how to start your labor at home. So my question is what's the difference between nipple stimulation and sexual intercorse.? Wouldn't intercorse help open the cervix more concidering a orgasm is a small contraction.? Correct me if I'm wrong because I am looking for answers. (I don't want my little man to come early I was just wondering).