In 533 women with normal pregnancies, taking fish oil (capsules containing 2.7 g omega-3 PUFAs/d) during pregnancy (from week 30 through delivery) was associated with a reduced risk of asthma in the child, as compared to a placebo (olive oil capsules), or no therapy. Of the 523 children that were followed for 16 years from the time of childbirth, 19 were diagnosed with an asthma-related disease, of which 10 were diagnosed with allergic asthma. Children of mothers who supplemented with fish oil were found to have a 63% lower risk of developing asthma and an 87% lower risk of allergic asthma, compared to children of mothers who had been given the placebo (olive oil) capsules. The authors conclude that supplementation with "omega-3 PUFAs in late pregnancy may carry an important prophylactic potential in relation to offspring asthma."
Asthma has a genetic component. If only one parent has asthma, chances are 1 in 3 that each child will have asthma. If both parents have asthma, it is much more likely (7 in 10) that their children will have asthma.
In addition to preventing asthma, fish oil during pregnancy can prevent post partum depression.
"Fish oil intake compared with olive oil intake in late pregnancy and asthma in the offspring: 16 y of registry-based follow-up from a randomized controlled trial," Olsen SF, Osterdal ML, et al, Am J Clin Nutr, 2008; 88(1): 167-175.