It's really crazy how much the internal os and the rest of the cervix dilates during childbirth. There is a big difference between 10 centimeters and just a few millimeters! And then afterwards it mostly goes back to the way it was before. Amazing!
I have to wonder about the internal os after childbirth though. Are women who have had children slightly prone to more bacterial infections because their internal os is open a little bit? Or does that small opening not even matter?