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Old 05-29-2011
heights's Avatar
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Question Why doesn't RhoGam bind to the baby's RBCs?

RhoGam is a IgG anti-RhD that bind to fetal RhD+ red blood cells that enter the maternal circulation when there is transplacental fetomaternal hemorrhage. It is given so that the foreign baby's cells in the mom's blood can be killed before the mom starts making antibodies against them. I get that part. My question is this: since RhoGam is IgG, why doesn't it cross the placenta and affect the Rh+ baby when it is injected in the Mom during pregnancy??
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Old 05-29-2011
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I think RhoGAM given at 28weeks of pregnancy is IgD and that which is given within 72hours after delivery is IgG type.

As the RhoGAM given during 28weeks of pregnancy is IgD, it doesn't cross the placenta.

The IgG RhoGAM given within 72hours after delivery is given in such low doses that it induces lysis of just about 15ml of RBCs (=30ml of whole blood) which cross placenta. therefore these antibodies do not remain till next pregnancy.

*Ethics related point i would like to add to it is that RhoGAM is a ''BLOOD PRODUCT'', therefore, the patient must give consent to receive this injection.
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Old 05-29-2011
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Quote:
Originally Posted by heights View Post
RhoGam is a IgG anti-RhD that bind to fetal RhD+ red blood cells that enter the maternal circulation when there is transplacental fetomaternal hemorrhage. It is given so that the foreign baby's cells in the mom's blood can be killed before the mom starts making antibodies against them. I get that part. My question is this: since RhoGam is IgG, why doesn't it cross the placenta and affect the Rh+ baby when it is injected in the Mom during pregnancy??
Good question!

the anti-Rh(D) [RhoGAM] is IgG...
"These findings indicate that the placental passage of anti-D immunoglobulin does not produce haematological changes relevant to haemolysis."

Maternal anti-D prophylaxis during pregnancy does not cause neonatal haemolysis
Author: Schwartz, T; Merlob, P; Maayan-Metzger, A; Sulkes, J
Archives of disease in childhood. Fetal and neonatal edition Vol: 84 Issue: 1 ISSN: 1359-2998 Date: 2001 Pages: 2 - F62

full text attached
Arch Dis Child Fetal Neonatal Ed-2001-Maayan-Metzger-F60-2.pdf
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Old 05-29-2011
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RhoGam is definitely IgG, not IgD (it's anti-IgD). The article Bebix posted is basically a study showing that even when it 's given in a high enough dose and crosses the placenta (as shown by positive direct Coombs test), it doesn't harm the fetus. Doesn't answer the question of why this is so, but at least we know that it can cross the placenta.
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Old 05-29-2011
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Default IgG, not IgD

I seem to have got it wrong. RhoGAM is IgG only. I actually studied it in the older edition of Kaplan immunology. now i corrected it after going through the new edition. thank you heights and bebix.
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Old 07-21-2011
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IF mother RH negative and baby RH positive , and in her last pregnancy we gave her RHoGAM at 28 weeks and postpartum , now( second pregnancy ) her antibody titer 1:256 do we need to give her RHoGAM at 28 weeks again or just only Postpartum ??
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