Peanuts may impact on the immune system
Mothers-to-be who eat nuts every day may increase their child's risk of developing asthma by 50%, claim Dutch researchers.
Nearly 4,000 pregnant women completed diet questionnaires, and their children were monitored for eight years.
The results, published in a US journal, suggest that potent allergens found in some nuts might prime the foetus to be allergy-prone.
Other studies, however, have been less conclusive about nuts and asthma risk.
The factors during pregnancy, or early life, that cause some children to develop asthma while others are unaffacted are still unclear.
Asthma runs in families, suggesting a strong hereditary link, but the environment still plays a significant role.
However, comparing women who ate nuts daily during pregnancy to those who ate them "rarely" consistently pointed to an increased risk, with between a 40% and 60% rise in the chances of wheeze, asthma symptoms in general, and use of steroids.
Dr Saskia Willers, from the University of Utrecht, who led the study, said: "While it is too early to make recommendations of avoidance, it is important for pregnant women to eat healthily, and what is true for many foods is that too much is never good."
The study examined the effect of eating different types of nuts, including peanuts, which botanically are not a true nut.
Peanuts have been closely associated with allergy.
"Peanut is a potent allergen, and peanut allergy is associated with anaphylactic shock and is less likely to be outgrown than other allergies."
The research also found lower asthma rates in the children of mothers who ate more fruit during pregnancy.
However, researchers suggested that other aspects of a healthier lifestyle followed by these women might be responsible.
The study was published in the American Journal of Respiratory and Critical Care Medicine, published by the American Thoracic Society.
Professor John Heffner, a past president of the society, said there was not enough evidence that the nut diet had caused the problem, and he called for more studies.
"These findings emphasise the critical importance of additional investigations into the environmental exposures for both mother and child."
Leanne Male, from Asthma UK, also said that further studies would be needed before firm dietary advice could be given to pregnant women, as other research had thrown up contradictory results.
She said: 'Some studies say that the vitamin E and other health properties nuts contain, especially when consumed as part of a healthy Mediterranean-style diet, can be protective against asthma."