Hello, I do not know of any studies to support this, but I agree with Kathy--you have more success when baby can breastfeed well before discharge.  Our NICU follows the Marjorie M. Palmer method of not introducing the bottle until 33 1/2-34 weeks.  If I or the nurse start feeds at the breast as soon as a baby is extubated, or if the baby gets a try at breastfeeding whenever the mother is available, we have pretty good success with getting babies home with effective breastfeeding.  Of course, nipple shields are hugely helpful, as well. We had followed up  about 40 mothers after discharge from the NICU.  Only one baby did not get off of the shield--but this baby did not bottle well either--I think there was more issues that were seen later than while this baby was in the NICU.  We still do a lot of supplementing for extra nutrients on discharge, but I did find the pumping is the first thing to get sacrificed, unless there is total commitment (and support) on the family's part to provide breastmilk and that the supply is excellent before discharge.  Still, there is a long way to go.  Maureen Allen RN, BSN, IBCLC, Boston, MA