it's always safe to have sex during pregnancy unless you are advised by your DR not to. I've never heard that you're not supposed to have sex in your 3rd trimester. My DR actually told me to have lot of sex to get the baby out. If you're unsure then always ask your DR and they will tell you what is best for your situation. Otherwise enjoy it while you still can.
You can have sex right up til the beginning of the 3rd trimester without causing any damage to you or your baby. Doctors recommend stopping sex after then in case it damages the cervix. Good luck with your pregnancy :) x
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.
As long as there are no complications in your pregnancy and it's preceding normally, sex isn't typically a problem. Some just find it uncomfortable or undesirable.