Pregnant women who eat low-fat yoghurt can increase the risk of their child developing asthma and hay fever, a study says.
At the European Respiratory Society conference, researchers will suggest this could be due to an absence of protective fatty acids in yoghurt.
The diets of more than 70,000 Danish women were analysed and their children followed until the age of seven.
Asthma UK says pregnant women should follow a balanced diet.
Pregnant women who ate low-fat yoghurt with fruit once a day were found to be 1.6 times more likely to have children who developed asthma by age seven, compared with children of women who did not eat low-fat yoghurt.
The study also found that the children of these women were more likely to have allergic rhinitis (hay fever) and current asthma symptoms.
But the results showed that milk intake during pregnancy was not linked to any increased risk of asthma.
In fact, milk was shown to protect against asthma development.
Ekaterina Maslova, lead study author form the Harvard School of Public Health, who worked with the data at the Statens Serum Institut in Copenhagen, said: "It is a puzzling finding. The absence of fatty acids in low-fat yoghurt may be key to the results.
"The results suggest that fatty acids play an important role or it could be that people who ate this kind of yoghurt had similar lifestyle and dietary patterns, but we cannot make any conclusions at this stage.
"We need to replicate these results in other studies first."
Leanne Metcalf, director of research at Asthma UK, said there is plenty of evidence to suggest that the pre-natal environment can influence a child's health.
"However, the impact of a pregnant woman's diet on her child's health continues to be debated, as it is difficult to assess how particular aspects of a woman's diet during pregnancy are linked to the risk of developing asthma and allergies.
"Eating a healthy, balanced diet at any time, but especially during pregnancy is advisable and we would recommend that pregnant women discuss any drastic changes to their diet with their GP first."