Michelle:  There is such a thing as "involution of breast tissue", which
may be permanent.  If the mom experienced trauma or severe, prolonged
engorgement without relief on that side, the body  can trigger this
involution.  In some cases it may be impossible to fully regain the same
capacity.  However, many women nurse off one side exclusively either
because of a medical problem (mastectomy) or because of needing to work
while wearing their babies (slings have a tendency to be worn so that the
mother's dominant hand is free).
Chris

 Chris Hafner-Eaton, PhD, MPH, CHES, IBCLC   email: [log in to unmask]
                HSR & Health Educational Consultant