Ellen,  I would say the cases of poor weight gain on the babies who only
breastfeed on one side was due to other reasons and when they switched over
to both sides that problem was resolving.
The breast are capable of producing more than enough milk for twins (even
triplets or more) and there are studies of women who only breastfed from one
side with their children thriving very well.
I tell mothers that the first side is the main course and the second side is
desert.  The baby should be allowed to stay on the first side until they
indicate they are done. Then the second side can be offered but not necessary
to have.  I also tell mothers to very attentive to their breast and if they
are getting full either feed the baby or express off some milk to keep
comfortable and avoid milk stasis.
Ann Perry RN, IBCLC
Boston, MA

             ***********************************************
The LACTNET mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software together with L-Soft's LSMTP(TM)
mailer for lightning fast mail delivery. For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html