Anti ABO antibodies in pregnancy

Going through UW's questions I found one that asks about ABO antibodies and alloimmunization during pregnancy (mother O Rh+ father AB Rh+ first pregnancy). Their answer says that antibodies to ABO antigens do not cross the placenta as they are IgM.

Goljan's Step 1 notes have the opposite explanation. They clearly say that anti AB IgG antibodies exist in some people without prior exposure and do cross the placenta and cause ABO hemolytic disease of the newborn.

I'm taking Goljan's word over UW's. Anybody know more?

[student-2]

The two answers are part of the same explanation!!! IgM if no Hx of previous blood exposure

[sarab]

IgM never cross the placenta it is right Goljan says this also, IgG can cross but not the IgM

[student-2]

The deal with Rh alloimunization is that the first exposure to Rh factor (duffy Ag) creates IgM. If this primary exposure is in pregnancy then IgG won't be in sufficient amounts to cause hydrops in this initial pregnancy because it takes a few months for seroconversion from IgM to IgG but in a second pregnancy with Rh- fetus hydrops will occur b/c IgG will be around and it can cross the placenta. Thats for RH factor!!!
As for ABO blood type- this is a phenomena- ABO antibodies exist only in IgM form and never progress to IgG. Weird but true. Hence the ability to give birth to a fetus with a totally different blood type. The ABO antibodies do form with no previous exposure. weird aint it.
Isn't nature fascinating!

[manleyjb]

Here is my understanding. ABO blood imcompatability can also cause HDN when mom is O and baby ia A, B, or AB. Sensitization is NOT required b/c IgG antibodies are naturally occuring in someone with O. Although, disease is mostly less severe the treatment is the same.