Re: Erythroblastosis Fetalis: communication between mother's and fetal blood

In utero, prior to delivery there is leakage of fetal blood cells into the
mothers circulatin.  This is minimal, and does not contribute a great deal 
to
the sensitisation of the mother.  The major sensitisation occors during
delivery.  Abortions amniocentesis,trauma etc. all can couse some
sensitising. By sensitising I ,ean the production of antibodies.  This is 
why
we give Rhogam to block the formation of maternal antibodies after all of 
the
above situations.  Prior to the advent of Rhogam, which is a bolus of
antibodies created and harvested from human donors, it took two or three
deliveries before serious problems occurred during a pregnancy.  Meaning 
that
it took several infusions of fetal blood to sensitise the mother.
The small amounts of leakage during a normal pregnancy is not enough to 
couse
troublesome reactions, but it is now used to do cromosomal studies in some
research inst. and  is a possible replacement for amniocentesis.
As to whether the antibody is IgG , or if only IgG is crossing the 
placenta,
is of no importance here, since we are talking about an antigen that is
attached to the red blood cell, and the whole thing  the blood cell, leaks
into the maternal circulatin.  RM