Putting on my med tech hat for now.

When an Rh negative mom gives birth to an Rh positive baby, there is a chance that small amounts of the baby's blood may get into her system at the time of delivery and trigger the production of antibodies by the mother against the Rh factor in the baby's blood.  In a subsequent pregnancy, these antibodies (which the mom will have forever more) can pass the placenta and into the baby's bloodstream where they will procede to destroy the baby's blood cells, if that baby is also Rh positive.  Rhogam is an injection of these same type of antibodies given to Rh negative moms during pregnancy and right after birth.  The purpose of it is to destroy any of the baby's blood cells which may have reached the mom's system before the mother's immune response can be triggered - kind of a blood-cleaning service.  After doing their job, the Rhogam is quickly broken down by the mother's body and disappears from the mother's bloodstream.  It used to be that Rhogam was only given after the birth.  However, a very small percentage of women get exposed to baby's blood during early pregnancy (and also during procedures such as amniocentesis) so many docs also administer a dose during pregnancy as well as after the birth.  If the mom gives birth to an Rh negative baby, then postnatal administration of Rhogam is not necessary.
Rh disease killed many babies before it was understood, so the use of Rhogam has been a great thing for all these Rh negative moms.  One of the most common antibodies that we pick up in the blood bank when screening older women (pre-Rhogam days) for transfusion is the anti-D (anti-Rh).

If it is determined that the father is also Rh negative, then Rhogam is not necessary because the baby will be Rh negative.  However, since 85% of the population is Rh positive and since the doctor never can really know for sure who the father is, Rhogam is usually administered routinely during pregnancy to all Rh negative moms.  I would imagine that in some countries, Rhogam is not being administered during pregnancy (the chance of being exposed to cells during early pregnancy is very low compared to exposure during the birth process).

Antibody production can also be triggered by ABO and other factor incompatabilities.  ABO problems are usually much milder than those caused by Rh, although occasionally a baby will end up with quite high bili levels from an ABO incompatability.  Type O individuals always have Anti-A and Anti-B in their blood - mostly IgM, but also small amounts of IgG.  This IgG can cross the placenta and cause problems for the baby, for instance, if a Type O mom is carrying a Type A baby.  Since the IgG anti-A is present even before the pregnancy, ABO problems can happen even with the first pregnancy.  With Rh factor, the Anti-Rh is not produced unless there has been an exposure, usually either through transfusion or pregnancy.

BTW, as has been previously stated, these antibodies would not survive passage through the baby's gut, so even if they were in the milk, it would not cause a problem for the baby.



Warmly,
Sharon Knorr, BSMT, ASCP, IBCLC
Newark, NY (near Rochester on Lake Ontario)
mailto:[log in to unmask]

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