I think we may have discussed this before but I have seen false birthweights
very often. Who knows how much this baby actually lost in the first few days
if he wasn't weighed. Does mom have nay pictures so you can evaluate just how
puffy he was at birth? He should begin gaining from the baseline you have
established. Weigh him again in a few days.
If a weight loss seems unusual when the baby prsents in the office,  I always
ask about labor interventions: Did she have an epidural? (OK that means she
got a minimum of 2000cc/ml of fluid before they started it) Did they use
oxytocin? More fluid. It can go on for ever.
I think one of my pediatric texts talks about the fluid filled infant of the
diabetic mother loosing large amounts of weight after birth.  It seems
logical that the same thing  could happen if the mom is overhydrated in
labor. Ever notice how some babies seem to have many wet diapers after birth
and very few, if any stools? That's why I worry more when a newborn isn't
stooling even when they are urinating well. (ala Niefert)
Marie Davis