bluestar
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I read from embryology today that fetal RBC can cross placenta to reach mom's circulation at late pregnancy. That means Rh+ Ag can reach a Rh- mom's blood can cause hemolytic anemia even before delivery. If this is the case, then how come it's always said that we expect to see hemolytic anemia until future pregnancy? anybody can explain this to me?
A question I saw recently is:
After the first delievery of a Rh+ baby, the Rh- mom is given Rh IG. 3 years later, she is pregnant with another baby and blood test shows that in her circulation there's anti Rh Ab, how come?
My question is if RhIG can't prevent Rb Ab from producing in future pregnancy, why are we still giving it?
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| mash
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in first pregnancy, fetal Rh Ag wud sensitize the mothers' immune system and first of all IgM Abs r produced which cant cross the placenta..
then class switching wud occur and mother will ve IgG Abs. so, in subsequent pregnancies the risk of hemolytic anemia in baby increases bcoz of preformed IgG Abs dat can cross placenta.
in case fetomaternal bleed has already occured due to previous abortion/APH , or mother has received transfusion earlier, she will ve anti Rh Abs. In dat case even first baby can ve hemolysis
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| dariush
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um surprised to see her develop Ab after 3 years b/c accord. to Katzung "...in Women treated w/ Rh0(D) IG, maternal Ab to Rh+ cells are not produced in subsequent pregnancies and hemolytic disease of the Neonate is averted.." (page 497)
??? where did you see this question bluestar ?
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| bluestar
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it's from NMBE. The reason that the woman develops RhAb could be "fetal RBC can cross placenta to reach mom's circulation at late pregnancy". But then from this logic, we should infer that woman should have Rh Ab from their very first pregnancy. But it's not the case.
I am so confused.
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| dariush
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bluestar i think what you`re saying is true that they start having Ab from the late first preg but if you think of it as an IMMUNE response, as it is, you know that always the primary response is mild and inefficient but once you develope the Ab you will have more immediate resistance as the Secondary response about all diseases. that is the rational behind any VACCINATION.
this i believe is a similar case in which supposing the 1st preg is the Primary response in which the mother simply doesnt have enough time to develop enough Ab to lead to a massive hemolysis.
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| tonguo
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the Tx for fetal hemolysis is RhoGam, which in reality is given twice to pregnant moms, once at about 28 weeks (not sure bout the exact timing) and another at delivery. so the first dosing would enable moms to eliminate RBCs leaked into maternal blood. so for the Q u mentioned, i think in her first pregnancy, there is no Ab formed because of this two-dose immunizztion. and Ab generated in the 2nd preganancy generated is just IgM, which dont cross placenta.
tong
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| dariush
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tonguo,r u sure about IgM not crossing the placenta? then the whole thing would make sense!!
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| tonguo
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i can assure u, dariush. only IgG cross placenta. IgM is a pentamer and too big to cross.
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| dariush
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thanx tonguo then everything is logical 
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