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How could maternal allergies affect preterm outcomes in infancy?

Recently, the prevalence of allergic diseases has been increasing. A large-scale epidemiological study showed that onethird of school-age children suffer from allergic diseases such as bronchial asthma (BA), atopic dermatitis (AD), allergic rhinitis (AR), or allergic conjunctivitis, and 5%–10% of children have multiple allergic diseases, suggesting that allergic diseases have become a significant health concern (Japan). In response to the increasing prevalence of allergic diseases, the Basic Law on Measures Against Allergic Diseases was enacted in 2014 (Japan). As one of the key messages, the law states the importance of epidemiological research as well as basic and clinical research to clarify the essence of allergic diseases. Further epidemiological studies are therefore required. The Japan Environment and Children’s Study (JECS) is a birth cohort study that identifies environmental factors affecting children’s health. In particular, the main objective of JECS, one of the largest cohorts in Japan, is to elucidate the effects of environmental factors during fetal and neonatal periods, which could provide invaluable data on the effect of maternal disease status, including allergic diseases, during fetal and neonatal periods on the fetus. In this issue of the journal, Kojima et al. reported the association between preterm birth and maternal allergy using JECS data and found that maternal BA and AR were associated with an increased risk of threatened abortion and preterm labor (PTL). In contrast, high total IgE levels were associated with a decreased risk of PTL. As for preterm birth (PTB), AR might have protective effects on early PTB with high levels of total IgE, although there was no significant association between allergic disease and PTB. They also showed a significant difference in the effects of AD and AR on early PTB by total IgE levels. Interestingly, atopic status with high IgE levels might positively affect preterm outcomes. As the authors discussed, Th2dominated immunological conditions could confer fetal growth advantages. However, the underlying mechanisms by which Th2-dominated immunological conditions positively affect fetal growth remain unknown. It also remains unknown why the effects on the fetus vary among allergic diseases by total IgE shown in the current study. Evidence is still lacking to answer how maternal allergies could affect preterm outcomes in infancy, and currently we are unable to see all the details of the answer. Hopefully, studies carried out using epidemiological, as well as basic and clinical, research will allow us to elucidate the whole puzzle of this question in the future, similar to discovering missing pieces of a puzzle.