"If you give the Rhogam antibodies during pregnancy you have just created the situation you were trying to avoid. The whole point is for the pregnant mother to NOT have antibodies against her own child circulating in her system while she is pregnant.
Any blood mixing would allow those antibodies to attack the baby.
It does not matter if the mother's immune system made those antibodies or another mother's immune system (rhogam) made those antibodies. They are identical down to their molecular structure and you do not want them to contact the baby" julieann199930
Like joybird said, this is not really accurate. Rhogam works like any vaccine, or also, kind of like a homepathic remedy. A little poison to confuse the immune system into protecting the person, but not a full blown immune response. I have a hard time putting it into words, basically when you are sensitized, you have a titer, anything above 1:1 is considered a titer. In one indiluted drop of blood, you can find the antibody. Then you dilute the blood by one drop of water, whenever you get to the dilution where the antibody disappears, that is your titer. It could be 1:32 or 1:500+ or lower or higher. A rhogam shot may give a mother a titer of 1:1 if she is pregnant right after getting a shot at the end of her last pregnancy, or it may never give her a titer. A titer strong enough to cause anemia would generally start at around 1:16 or 1:32. If its a second or more sensitized pregnancy, the titer may not matter. Titers can go up or down between pregnancies & during a pg. Rhogam definitely has some issues, but it can't truly sensitize a woman.
I used to get rhogam only afterwards, if the baby was positive only. Then, after a loss during delivery & a big bleed on my part, I got sensitized. I don't have any regrets about not getting prenatal rhogam. The bleed I had was so big that the rhogam pp didn't work at all. I have had 2 sensitized pregnancies, the first was worse than the second, although both boys are in great health now. Nowadays being sensitized is not the end of the world, but I have to caution that most midwives and OB's know very little about this & tend to have very old information. When new treatments for fetal anemia are discovered, things like IVIG & EPO treatments for mothers, only the perinatologists get invites to the conferences. Most peri's are not as scared of sensitized mamas as OB's & MW's are.
Sorry to write a book!