Sex in third trimester

So if you have a healthy pregnancy...

I know that sex can help induce labor at the very end but at what point, I mean at how far along do you worry about it stimulating labor too early. Or is it the kind of thing where it won't stimulate labor if your body isn t already gearing up for it anyways. And is it orgasm or the actual sex part that does it? Little backstory. My husband has been very put off by sex this entire time and I think He is finally coming around to the idea( now that im 29 weeks tomorrow go figure).