You can safely have sex as you get closer to your due date until your doctor says otherwise (or until your water breaks). Stop if it gets too uncomfortable or if you notice spotting or bleeding after intercourse. If that happens, contact your doctor and he or she should be able to determine the cause or suggest you come in for an evaluation.
Here are some best positions that wouldn't harm you or the fetus.
Lie on your side curled in a C, as your partner faces your back and enters your vagina from behind. Nice and cozy.
Lie side by side with your partner, facing one another. He slips his leg over yours (your leg is straight and to the side or bent at the knee) and enters you from an angle. Another good one for keeping his weight off your belly.
You get the picture. This one’s great for controlling the pace. (And don’t be self-conscious about your belly—it’s beautiful.)
Lie face-up on the edge of the bed, with your feet on the floor. Your partner stands or bends over you. Just make sure he doesn’t thrust too deeply.
Support yourself on all fours (on the bed or floor) as your partner enters from behind. Wonderful way to get some g-spot stimulation but again, beware of major thrusting.