Regarding mixing the two in one bottle: I alwasy tell moms not
to-not because of any specific harm to the contents, but if she
mixes and baby doesn't take the entire bottle, she will be tossing
out some of her valuable breast milk.  I suggest she (or whoever is
feeding baby) give whatever breastmilk is available, and then if
more is needed, give the formula.  The exception would be when baby
has a definite taste preference and won't take the formula alone
(smart kid!).
Our Visiting Nurses (who do our home follow-up for early discharges)
recently expressed concern about how many moms they saw either
combining or pumping and giving breastmilk by bottle.  I told them
that I felt these were mostly moms who would either do this or
totally formula feed.  While exclusive breastfeeding is what we'd
like to see all babies get, I would rather see a mom do SOME
breastfeeding or give her milk in a bottle than for baby to get no
breastmilk.
When a mom tells me one of these approaches is her plan, I don't try
to talk her out of it (I don't want to lose her entirely), but I
encourage her to start with exclusive breastfeeding to help her get
her suply established and to give baby the best possible start.  If
she is definitely going to give bottles, I recommend she wait at
least 3-4 weeks to reduce the potential for nipple confusion (or
whatever you want to call it).  Hopefully, at least some will be so
"hooked on" exclusive breastfeeding by this time that they may
reconsider their original plans.
Winnie Mading RNC, IBCLC

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