Taking a daily fish oil capsule during pregnancy and the first few months of breastfeeding may reduce a baby's risk of food allergy, research suggests.
According to a large analysis of past trials by Imperial College London, this led to a 30% reduction in egg allergy risk by the age of one.
Fish oil contains a special kind of fat called omega-3 that has a positive, anti-inflammatory effect.
Experts said larger trials were needed that followed up children for longer.
But they said the research confirmed that diet in pregnancy could influence the development of allergies in early life.
One in 20 children in the UK is affected by allergies to food, such as nuts, eggs, milk or wheat – and it's a growing problem.
These allergies are caused by the immune system malfunctioning and over-reacting to these harmless foods, and this triggers symptoms such as rashes, swelling, vomiting and wheezing.
Dr Robert Boyle, lead author of the research, from the department of medicine at Imperial College London, said: "Our research suggests probiotic and fish oil supplements may reduce a child's risk of developing an allergic condition, and these findings need to be considered when guidelines for pregnant women are updated."
The supplements contain omega-3 fatty acids, which are also present in oily fish.
Current advice is that pregnant women should eat no more than two portions of oily fish per week because of the levels of mercury in some fish, and avoid shark, swordfish or marlin altogether.
The researchers looked at 19 trials of fish oil supplements taken during pregnancy involving 15,000 people, finding that the reduction in allergy risk equated to 31 fewer cases of egg allergy per 1,000 children.
They also looked at the impact of probiotic supplements taken during pregnancy and found a 22% reduction in the risk of eczema developing in children up to the age of three.
But they found no evidence that avoiding foods such as nuts, dairy and eggs during pregnancy made any difference to a child's allergy risk.
Fruit, vegetable and vitamin intake appeared to have no impact either, the study published in the journal PLOS Medicine found.
'Further larger trials'
Seif Shaheen, professor of respiratory epidemiology at Queen Mary University of London, said the research added to the growing evidence of a link between diet during pregnancy and breastfeeding and preventing childhood allergies.
"More definitive answers on the possible role of maternal probiotic and fish oil supplementation in the prevention of childhood allergic disease can only come from further large trials which follow up the children to school age," he said.
"If such trials are big enough, they may be able to identify particular subgroups of mothers and children who would benefit most from these interventions."
Dr Louisa James, of the British Society for Immunology, said there were still questions to answer over the impact on severe food allergies, not just a sensitivity to eggs.
"The studies using fish oil supplementation all measured allergic sensitisation to egg as a surrogate measure of food allergy," she said.
"Although sensitisation is necessary for allergies to develop, many children may be sensitised without ever developing any symptoms of allergy and so it will be important to determine if fish oil supplementation can reduce the risk of clinical food allergy."