Several in vitro studies have suggested the presence of Th2-skewed immunity during pregnancy in infants with atopic diseases. Our study indicated that allergic infants showed a higher birth weight and shorter gestational period at birth than those of non-allergic peers. Moreover, allergic mothers gave birth to neonates whose birth weights and gestational ages were higher and shorter than those of the non-allergic mothers, respectively. Thus, our data clearly demonstrated the promotion of intrauterine growth, either in the allergic children, or allergic mothers. Such an intrauterine environment favorable for the fetal growth may also accelerate the development of allergic diseases in their offspring that are most probably caused by the Th2-oriented immunity.