Same thing is happening to me and they do not seem worried at all. We talked about it today, actually, and they said its seen in first time mothers often and sometimes they do not see a change until labor. Your cervix is esentially the bottom/or opening of your uterus. So when it does dilate all the way it should open to your birth canal/Vagina. Actually it isn't that it doesn't lead there now, its just behind the babies head, which is now lower than the cervix. Once your cervix ripens more the 'opening' should move lower and widen.
Karen Mommy of McKenna 2003 & Alysson 2004 Expecting an early Christmas Present