With reference to the question,

"Shouldn't ABM stand for artificial breastmilk not artificial baby milk?"

I think this is another example of a "Britishism".  I have noticed on trips
to the UK that this term is used.  Also "BM" does not have the same fecal
connotations it has in the US.  Although I have always considered myself a
native speaker of British English,  all my children were born in the US and
 I realised (realized) when answering some of my cousin's pregnant wife's
questions about breastfeeding, that in England I just don't speak
breastfeeding.  I had to rush out and procure a copy of THE WOMANLY ART from
a London League Group and do some swatting (British for studying).  I
remember being extremely shocked when my mother-in -law first offered to
"nurse" my baby... after all she hadn't nursed her own!

Cheerio.
Lesley Robinson, IBCLC, LLL Leader
Corning, NY (formerly of North-west London)