The authors suggest this due to different conditions in the uterus. They recruited more than 1,200 newborns form the Isle of Wight, recording their birth order and taking samples of cord blood IgE, and conducting skin prick tests at ages four and 10.
They found variations in the IL-13 gene were associated with a statistically significant higher relative risk of having increased cord-blood IgE – an indication of increased allergic response.
‘This is the first study to test whether the effect of genes involved in the development of asthma and allergy differs between first- and later-born children,’ said the authors.
‘This finding may partially account for the increasing prevalence of asthma and allergies in children in the last 30 years, primarily seen in the western world, as developed nations’ birth rates continue to decline,’ they said.
The research was presented this week at the American Thoracic Society’s international conference in Toronto, Canada.