TMI--Embarrassing Question

Anna
Please try not to laugh at this. I am 38 weeks and last was checked last Friday and was 2cm dilated. I've heard it is safe to continue to have sex as long as your water hasn't broken. Last night my SO and I did (TMI TMI TMI) while he was on top, I could feel her body moving in the same motions as he was. Should I be concerned? My reason for thinking maybe I should be is because the doctor is able to tell I am dilated and is able to feel the baby. So wouldn't that mean he would reach that point?