In a case-control study involving subjects from the Children's Health Study, researchers found:
The risk of asthma in children born to mothers with a history of asthma who ate oily fish at least monthly to be 80% less than children whose mothers did not eat fish during pregnancy. However, children born to non-asthmatic mothers did not appear to benefit from the moms eating fish. On the other hand, the study found that for those moms that ate fish sticks during pregnancy—a source of unhealthy trans-fats—the risk of asthma in their children was doubled.
This study suggests that consumption of oily fish by pregnant women with asthma may offer a dramatic protective effect against their offspring getting asthma.
"Maternal fish consumption during pregnancy and risk of early childhood asthma," Salam MT, Yi YF, et al, J Asthma, 2005; 42(6): 513-8.