I heard Susan Browne, MD IBCLC, give a panel on breastfeeding and allergies
at a LLL conference a few years ago and she mentioned a study of infants with
a cow's milk allergy.  Supposedly the infants had not been exposed to cow's
milk until the time they had the reaction. It was though that in utero
exposure set off the reaction but it was later found that 72% had received
formula in the first 72 hours in the nursery and their mothers were not aware
of it.
  Susan could give you more details but I don't know how to  contact her.  I
believe she's in NY.
Lezlie Densmore, LLLL