Yes, with a few exceptions. It's not safe if you're bleeding or have a placenta that's in front of the baby's head — they call this placenta previa. With placenta previa, if the penis comes in contact with the cervix or you have contractions as a result of orgasm, it can traumatize the placenta and cause significant enough bleeding that you lose the pregnancy. Also you shouldn't have sex if your membranes are ruptured (water breaks) because then the baby is no longer protected against any possible infection. It's also risky to have sex if it's early in your third trimester and you're having premature labor or you have a short cervix, because an orgasm can stimulate contractions. But if you're having a healthy normal pregnancy there's no risk, though as you get larger, it may be uncomfortable, requiring you to be creative about your position.