I would suggest pushing the formula now- even just one bottle a day- until they get the results back- it will prevent the numbers from climbing too high and even if it is not necessary it will help baby get used to a bottle and the taste/smell of the formula. If you can afford it i would strongly suggest you find yourself a good double electric pump (i got a freestyle and it has worked well) so she can pump while feeding the bottle. If she doesn't keep up her milk supply then there is a chance that she could lose her milk (b/c when it comes back that she can only nurse 1-2x per day it will be too much of a shock to the system!) and i'm guessing breastfeeding is imporant to her.
It sounds daunting and impossible but it will be ok. Chances are he will be just as big and strong (maybe even moreso) than non pku. My little girl is onpar for her weight and they say that pku ers usually have better muscle tone. Phe is one amino acid in protien. There are many more. The formula has all of the other amino acids – just not phe…..in the normal person's body phe is broken down into Tyr. So the formula has extra tyr added b/c pku bodies cannot do the phe to tyr conversion. At the end of the day baby is getting the same stuff regardless.
I breastfeed and it is very hard- espeically b/c i have two other little ones- but they say breastmilk increases iq by up to 10 points and pku decreases iq by 10-15 points so i figure if i nurse baby should be extra ok- right? I just pumped my extra milk and donated it to a family who needed it (baby was allergic to formula). It took a lot of hard work but was worth it.