I work in a Behavariol Medicine facility, and when I go over HPI elements with my physicians I tell them since our facility is for mental health that location (head) would NOT be a good reference to use unless they are coming in due to maybe cognitive deficits due to a TBI or CVA, or a recent head injury that is causing cognitive problems.
So I am taking it that your practice is an OB.GYN so I would agree that pregancy at how many weeks would not be good to use for duration and location.
As for documentation stating that you should not use those I don't know of any. But I would say that the situation would call for the type of practice you are in and coding for.