Sensitization does not develop in utero

Background: Intrauterine sensitization has been suggested to play a role in the development of atopic disease in children, and this has led to current guidelines recommending allergen avoidance during pregnancy. Objective: To investigate the relevance of allergen-specific IgE in cord blood to sensitization in early infancy and the origin of such IgE. Methods: Inhalant and food allergen-specific IgE in cord blood was analyzed and compared with specific IgE in infant blood at 6 months of age and in parental blood. Cord blood IgA was measured to detect maternal blood contamination of cord blood. Results: Allergen-specific IgE, primarily against inhalant allergens, was detected in 14% of cord blood samples. However, corresponding specific IgE was not found in infant blood at 6 months of age. Specific IgE in cord blood completely matched specific IgE in maternal blood with respect to allergen specificity, level of specific IgE, and ratio of total IgE/specific IgE. Finally, there was a correlation between specific IgE and IgA in cord blood. Conclusion: Allergen-specific IgE in cord blood does not reflect intrauterine sensitization but seems to be the result of transfer of maternal IgE to the fetus.