JACI has a paper in press that addresses this important question. The background is that allergen induced T-cell reactivitiy has been shown in cord blood – a strong argument that sensitization occurs transplacentally. Genotyping of these cells confirmed their fetal origin. It is unclear, however, if this is only a transient (normal?) reaction – and mothers want to know if they need to avoid for example peanuts during pregnancy. Rowe et al. now arrive at a clear conclusion
These findings question the scientific basis for existing recommendations for allergen avoidance by high-risk women during pregnancy
Lets have a look at their key result – figure 2B top right:
Only when redrawing their results, I found that the cord blood values are missing from the plot – which certainly weakens their findings. Furthermore we can see 2 individuals (marked with “A” and “B”) that had elevated HDM IgE levels at 6 months and continued to have high values. So, I would slightly modify their conclusions to
Allergen sensitization of the embryo is not the rule but may occur
If you want to follow this fascinating field here are two links: Prof. Holt’s group & a new immune tolerance study