Rhogam

[MissMedicine]

hi guys

do you guys know what would be the reason why a mother who was given rhogam during her first pregnancy who test + for anti_D ab's in her serum during her second pregnancy?

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[tg78]

Exposure to the blood of her second baby (intrauterine hemorrhage or something like that). I think...

 

[barone ROCKS]

i know it sounds redundant but it could be a number of reasons from too much D+ ag for the rhogram to handle to the mistiming of the rhogram. you have to give rhogram twice during pregnancy, i think the first time is in the second trimester and the 2nd time is around delivery.

 

[Idiopathic]

I want to know why the anti-D IgG in Rhogam doesnt cross the placenta and knock out all the babies blood.

 

[starayamoskva]

I would say it would be due to exposure to blood from the current fetus. This is why Rhogam should be given at 28 weeks gestation and after delivery. Additionally if the mother experiences any bleeding ie threatened AB. Of course it could be that she had a miscarriage between the first and second pregnancy that she was not aware of; wrote it off as a heavy period not realizing she had been pregnant.
Hope that helps

 

[MissMedicine]

thanks!!! so why isnt it bc of residual rhogam? is that just dstroyed by the spleen eventually

 

[Idiopathic]

It could be. IgG does have a long half-life in the body. I am not sure that 'old' antibodies are destroyed in the spleen or not. They may just deteriorate and get digested by proteases.

 

[MissMedicine]

well its either one or the other... theres only one answer to the q

 

[Idiopathic]

It is probably not due to blood from the current fetus, because the fetal blood only makes it into materanl circulation if there is a bleed (usually during childbirth) and so is not a problem otherwise. Remember, RhoGam is given to bind up any antigen to prevent maternal antibody from being made.

 

[MissMedicine]

yea it didnt seem to be a complicated pregnancy so I dont know how a hemorrage is the "most likely" scenario... so youre saying its probably bc there is residual rhogam?

 

[Idiopathic]

Yes.

 

[jakstat33]

Hey Idio- who's this Iatrogenic cat??? they've been prancing around, posting here and there while you've been gone... don't they know that the Step 1 Forum is all about IDIOPATHIC?? c'mon now, iatrogenic?! I think you need to do something about this... get 'em IDIO

 

[Idiopathic]

Hey Idio- who's this Iatrogenic cat??? they've been prancing around, posting here and there while you've been gone... don't they know that the Step 1 Forum is all about IDIOPATHIC?? c'mon now, iatrogenic?! I think you need to do something about this... get 'em IDIO

Someone who didnt know what First Aid was, for starters...

Oh well, 'physician-induced' could often be mistaken for 'of unkown origin', but not in this place(!)

 

[djipopo]

I want to know why the anti-D IgG in Rhogam doesnt cross the placenta and knock out all the babies blood.

just an FYI -- the 1st shot given at ~28 weeks is anti-D IgD (that way it won't cross the placenta), then the shot given after birth is anti-D IgG.

HTH

 

[Idiopathic]

Thank you...I have been stewing over that for the longest time.

 

[MissMedicine]

so is there a consensus that it's bc of residual rhogam that the mom is ab+ during the second delivery... so isnt this residual ab harmful to the next baby? im confused??!

 

[BellKicker]

so is there a consensus that it's bc of residual rhogam that the mom is ab+ during the second delivery... so isnt this residual ab harmful to the next baby? im confused??!

MissMedicine,

Sorry to jump in like this but there's no way residual Rhogam would cause the mom to be antibody positive. You could pump a liter of rhogam into a rhesus negative patient and she wouldn't generate a memory B cell response.

I'm sure it must have been because there was too much fetal blood in the maternal circulation during the first delivery. There's that German sounding test (Kleihauer-Behtke) that measures the amount of fetal red cells in the mom. The standard dose of 0,3 mg of rhogam eliminates 15 mL of fetal cells. It seems plausible that once in a while a patient is given too little rhogam.

The other possibility would be that the mother got exposed to the rhesus antigen in some other way, through a transfusion or from the second baby.

Looking back at your post, maybe I misunderstood something. Where did a second delivery suddenly come from? My above post makes more sense in response your original question, I guess.

 

[Idiopathic]

IgG from the second rhogam dose can linger in the mom. No doubt about it. I would bet money on residual antibody (not humoral immune response) rather than the mom mounting an antibody response to the current baby, without some indication of complication.

 

[BellKicker]

OK, that would be an amazingly long-lived dose of rhogam, then. I guess theoretically it could happen but does antibody stay in your system for that long? Even if the mom got pregnant right after the first baby, we're talking almost a year.

Also, why would this cause fewer complications than an endogenous response?

Idio, I think you're listening for the hoof beats of the proverbial zebra.

I'm still saying the first baby bled more than 15ml of erythros. Or someone made a mistake. Or she was transfused. Or she mixed blood with her high school boyfriend. Or the current baby's cells made it across to hers.

 

[MissMedicine]

ok the choices for the mom being ab+ during the second pregnancy are :
-intrauterine transplacental fetal-maternal hemmorage with second pregnancy
-residual rhogam

oh yea, and the question says the second delivery is x years later (not saying exact years bc, well ya know, to be safe)

i think youre right bell, the stem seems to suggest by stating the number of years later, that Abs are probably not lingering around.

 

[starayamoskva]

ok the choices for the mom being ab+ during the second pregnancy are :
-intrauterine transplacental fetal-maternal hemmorage with second pregnancy
-residual rhogam

oh yea, and the question says the second delivery is x years later (not saying exact years bc, well ya know, to be safe)

i think youre right bell, the stem seems to suggest by stating the number of years later, that Abs are probably not lingering around.

This is a long post. The gist of it for those who don't want to read it, is that giving the mother Rhogam is not a 100% guarantee that she won't get isoimmunized.

Rhogam btw is IgG with a small of amount of IgA, the type given in early pregnancy is not IgD. It doesn't effect the fetus because the amount given to the mother is only enough to neutralize about 15cc of fetal blood, only a very small amount of that would cross the placenta and if it had any impact on the fetus it would be miniscule.

Supporting data:
http://www.drugs.com/PDR/MICRhoGAM_Ultra_Filtered.html

Essentials of Obstetrics and Gynecology:
...the greatest risk for fetal-to-maternal hemorrhage occurs during labor and delivery, Rh immune globulin was initially administered only during the immediate post partum period. This resulted in a 1% to 2% failure rate, thought to due to exposure of the mother to fetal red blood cells during the antepartum period. The indications for the use of Rh immune globulin have therefore been broadened to include any antepartum event (such as amniocentesis) that may increase the risk of transplacental hemorrhage. THe routine prophylactic administration of Rh immune globulin at 28 weeks grstation is now the standard of care. This approach remains controversial for some practitioners because of concern about its cost effectiveness and the safety of the volunteers who are used in the commercial production of the vaccine. Despite adherence to this suggested RhD immune globulin protocol, it is reported that 0.27$ of primiparous Rh-negative patients still become sensitized.
During a normal preganancy 300 micrograms of Rh immune globulin is administered at 28 weeks gestation following testing for sensitization with an indirect Coombs test. A 300 microgram dose is administered following amniocentesis at any gestational age. If a feto-maternal hemorrhage is suspected at anytime during the preganancy a Kleihauer-Betke test should be performed. If positive, Rh immune globulin is administered in a dose of 10 micrograms/ml of fetal blood that entered maternal circulation. Following an uncomplicated delivery, 300 micrograms of Rh immune globulin is given within 72 hours.
Establishment of fetal circulation occurs at approximately 4 weeks gestation and the presence of the Rh (D) antigen has been demonstrated as early as 38 days following conception. Consequently, Rh isoimmunization can occur at any time during pregnancy from the early first trimester on.
Because fetal erythrocytes can be readily detected in the maternal blood following spontaneous or induced abortion, 50 micrograms of Rh immune globulin should be given to all Rh-negative women following any type of abortion (including tubal pregnancy).

 

[MissMedicine]

lol, not to be blunt but whats the right answer to the question?

 

[starayamoskva]

lol, not to be blunt but whats the right answer to the question?

Since I don't know the answer choices, I can only give you what the possibilities would be, now if one of the following was an answer choice you are all set.

There was exposure to fetal blood at some point in the current pregnancy.

There was a miscarriage/abortion between the first and second pregnancy that she did not receive Rhogam with.

The dose of Rhogam given after the first pregnancy was not sufficient for the amount of fetal blood in her circulation.

She was one of the unlucky 0.27% of people who get isoimmunized even with adequate treatment.

 

[starayamoskva]

It could be. IgG does have a long half-life in the body. I am not sure that 'old' antibodies are destroyed in the spleen or not. They may just deteriorate and get digested by proteases.

The half life of IgG is 7-23 days. The reason that IgG levels remain in the blood for years is because they are continually being made.
This is not the case with Rhogam which is an exogenous IgG.

 

[djipopo]

[/QUOTE]Rhogam btw is IgG with a small of amount of IgA, the type given in early pregnancy is not IgD. It doesn't effect the fetus because the amount given to the mother is only enough to neutralize about 15cc of fetal blood, only a very small amount of that would cross the placenta and if it had any impact on the fetus it would be miniscule. [/QUOTE]

interesting, i was told about the Ig D thing from one of the Kaplan professors last month, maybe it's a new preparation?

 

[MissMedicine]

Since I don't know the answer choices, I can only give you what the possibilities would be, now if one of the following was an answer choice you are all set.

There was exposure to fetal blood at some point in the current pregnancy.

There was a miscarriage/abortion between the first and second pregnancy that she did not receive Rhogam with.

The dose of Rhogam given after the first pregnancy was not sufficient for the amount of fetal blood in her circulation.

She was one of the unlucky 0.27% of people who get isoimmunized even with adequate treatment.

yes your first option was a choice (see one of my previous posts where I list the choices) but the question stem didnt seem to suggest this was a complicated pregnancy but I think you are right.. i am very reluctant to believe that the ab from the prophylaxis sticks around after several years.

 

[Ursus Martimus]

just an FYI -- the 1st shot given at ~28 weeks is anti-D IgD (that way it won't cross the placenta), then the shot given after birth is anti-D IgG.

HTH

First off, Rhogam is in no way IgD, do you know how much free IgD there is around to purify and make drug out of? The D antigen is actually only one part of the multimeric Rh antigen. As always the devil lies in the details of what they don't really tell you in medical school. It should be mentioned that of all the human IgG subtypes: ie. IgG1, IgG2a, etc, not all of them are capable of being transported across the placenta, so the fact that IgG crosses the placenta is one of those gross generalizations, that in this case matters. Also there are all kinds of situations for which there may be microbleeds across the placenta (abruption, previa, amniocentisis, etc). Women are often given a dose, when there is a mismatch, at 28 weeks and again within 72 hours of birth, or when one of the events list before occurs.

 

[djipopo]

First off, Rhogam is in no way IgD, do you know how much free IgD there is around to purify and make drug out of? The D antigen is actually only one part of the multimeric Rh antigen. As always the devil lies in the details of what they don't really tell you in medical school. It should be mentioned that of all the human IgG subtypes: ie. IgG1, IgG2a, etc, not all of them are capable of being transported across the placenta, so the fact that IgG crosses the placenta is one of those gross generalizations, that in this case matters. Also there are all kinds of situations for which there may be microbleeds across the placenta (abruption, previa, amniocentisis, etc). Women are often given a dose, when there is a mismatch, at 28 weeks and again within 72 hours of birth, or when one of the events list before occurs.

if you would have scrolled up a few posts you would have noticed my correction and the source of the erroneous info.

that said, thanks for your enlightening contribution.

 

[roady]

Thanks for posting these questions, MissMedicine--and for the lively discussion (old Moscow especially--blyat! Otleechno!!!)