Patricia, you are right in saying we do not yet have the studies to show
that silicone nipple shields reduce milk supply, but the Woolridge et al
1980 study and the Jackson 1987 study on latex shields did show reduced
milk transfer. There are several other studies cited in Riordan and
Auerbach which show milk volumes are less with the use of shields - and if
milk yield (ie removal)  decreases we can conclude with some confidence
that milk production will be affected.

This may not matter if the nipple shield is only used for a short time. It
may not even matter if it is used long-term - we have all known mothers use
shields for weeks and weeks without it  making their milk supply
inadequate, though I know I and many others  have also known mothers who
have used a nipple shield long-term and only acheieved an adequate supply
when the shield is no longer used. We cannot be certain that the silicone
nipple shields in use today have the same effect as latex ones (though I
cannot see why they would not have at least a similar effect - they're
basically the same shape and work in the same way).

On balance, surely we have enough experience and reasonable-quality
evidence to say that if a mother is using a shield long-term, and she is
concerned about milk supply, then an important step to increasing the milk
is for the baby  to come off the shield.  Clearly, I don't expect this to
be done at the expense of the baby getting breastmilk - if the baby can't
feed w/o the shield, then the whole process has to be done carefully,
sensitively and protectively.

The mother in the original post had been using nipple shields from the
start of bf, and the baby was now 2 wks (can't check all the details - I
have deleted the post, sorry) .  There was concern about milk supply. Why
not work towards getting rid of the shield so normal, physiological milk
production and supply can take place?

Honestly, folks,  I didn't know I was being controversial here!   Am I?

Heather Welford Neil
NCT bfc Newcastle upon Tyne UK