As a former employee of a pump company, I have to put my .02 in here: Because the mechanics of a baby removing milk from the breast include jaw compression, and the mechanics of pumping rely solely on nipple stim to initiate letdown and then suction removal of milk, is it similar or not? My guess is that the baby will always be more efficient at milk removal, but pumping to stimulate and remove milk will maintain milk production adequately. When I worked in a hospital as LC, we always noticed a decrease in supply of moms pumping for premies when baby had not been to breast yet. Also, the flexible shield offered by one or two pump companies is marketed as "increasing prolactin levels thus allowing greater milk production." Now don't quote me verbatim because there are several generations of new pumps out that I have no experience with. But the original concept of pumping is as described above - and I will visit all the companies at the conferences this summer to learn more. Thanks for listening Mary Kay Smith, CLE, IBCLC Romeoville, IL