A study by researchers at University of Oulu, Finland, found that children born in October or November were twice as likely to have food allergies as children who were born in the spring or summer.
Other studies in Sweden, the Netherlands, and Japan have found similar patterns. Researchers think that the cause may be the mother's exposure to high levels of birch pollen (highest in April and May) during the 11th week of pregnancy. 11% of children whose 11th week of gestation was in April or May had positive skin prick tests for food allergens. For children whose 11th week was in other moths, the rate ranged between 5.5% and 8%.
Researchers caution that higher rates of sensitivity could also be due to different levels of exposure to viruses and sunlight, at different times of year. It is possible that the mother's lack of vitamin D or exposure to seasonal viruses might affect the development of the immune system.
Should you plan your pregnancy to avoid spring pollen? Results are not yet clear enough to caution against getting pregnant in January or February.