Betty Dodson with Carlin Ross
Better Orgasms. Better World.
Here is another link to a Ph.D. sexologist, Danielle Harel, who did her dissertation on sexualizing labor and birth.
I wanted to make her info available, but I want to comment on what I consider to be oversimplifications to the concept of increased arousal and increased stimulation in several of her statements. This is getting into the minutia of sexual technique and any time you move down into the details, I consider them advanced sex concepts. As Betty often says to me, "Goddess is very often in the details."
Here are three links to sites that have info on this largely unknown topic in women's sexuality:
Here's an article on sensual birth options with many fine links to more sources.
And this is from a favorite site of mine that discusses sex/intercourse/making love during labor.