I had 6 IvIgg treatments during the last 5 weeks of my last pregnancy
for a rare blood disorder where my blood destroys babies' platelets in
utero.  The doses I got took 5 hours each and were very high to ensure
it crossed over to the baby.  I researched Igg pretty thoroughly - the
CDC guidelines I saw indicated that Igg prepared in the U.S. has to go
through procedures (freezing I think) that destroys HIV/hepatitis, etc.
So it is safe.  However, the potential side effects I experienced from
the treatments include high fevers, chills, panic attacks, contractions
and projectile vomiting (not common to have all of them, but I did) and
the baby experienced tachycardia for about 12 hours after each
treatment.  Another woman I knew who had the treatments would develop
bacterial meningitis after a treatment.  No doctor/nurse/anyone ever
even ventured that nursing would be risky.  If I had to have a treatment
now, I personally wouldn't nurse during the treatment.  But that's the
only restriction I can imagine.  IvIgg is the standard treatment for
pregnant women whose babies have neonatal alloimmune thrombocytopenia.
If it's safe for pregnant women to cross over to babies, then it has to
be safe to bf.  For more info on this to use as evidence, look up
research by Dr. James Bussell at New York Hospital/Cornell University.
He's the primary NAT researcher in the world and has studied pregnant
women on IvIgg for years.  If IvIgg weren't safe, I would assume they
would do early csections instead of trying to keep these babies growing
in utero during the treatments.
Mary