Sex and Labor Induction
In fact, sexual intercourse at term may help bring on the onset of labor. Part of what makes that happen are the prostaglandins in semen. The prostaglanids hit the cervix, which sends a message to the brain to release oxytocin. Oxytocin tells the uterus it's time to contract.
If you have sex during this time in pregnancy and either bleeding ensues (not just spotting) or the contractions increase in intensity and become stronger after sexual activity has ceased, you should call your doctor for advice.