Shrinking Size of Scanned PDF documents?

I use scanned forms for storing medical records in an office setting.  There is one form that is often modified.  So, the form with printed key sections is printed and then filled in with handwriting.  It is then scanned.  That same form with the handwriting is then printed when the patient returns, and again handwritten additions are made.  After a number of rounds of this use, the result is an increasingly small end result of the scanned form so that it is too small to be read.  Can you tell me how to avoid this shrinkage problem?

  Thanks.