completely safe till your waters break :) i had sex on my due date, not that i wanted it just to get baby out haha!
Until your water breaks. I had sex until the end even at 3 cm dilated. Plus it helps with dilation and orgasms help with jump starting contractions.
Im pretty sure its safe to do it right to the end! It just might be a bit uncomfortable but its safe. And the prostaglandins in the sperm might help to induce your labor!
If your having a normal and healthy pregnancy then it is fine to keep having sex. If you are having a problems...consult your doctor.