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A mother who has toxoplasmosis gives birth to an ...

Antitoxoplasma IgM antibody concentrations

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submitted by hayayah(603),

The baby does not get any maternal IgM, IgA or IgE as they do not cross the placenta, so if IgM is found it may suggest the baby has encountered an infection in utero.

IgG is passed down to the baby as a means of passive immunity until the baby can form their own antibodies of different types. So if you see anything other than IgG (e.g. IgM) you know it must be d/t an infection.

hungrybox  The baby gets IgA via breast milk. +1  
mbourne  @hungrybox, this is true. However, IgM antibodies are the first antibodies endogenously produced before class-switching occurs. So IgM antibodies in a newborn suggests infection. +1