High levels of sugar consumption during pregnancy doubled the chances of a child developing allergic asthma, the study of almost 9,000 mother-child pairs showed.
Allergy risk was increased by up to 73 per cent, but no link was found between sugar exposure in the womb and rates of eczema or hay fever.
The team compared the 20 per cent of mothers who consumed the most sugar when pregnant with the same proportion who consumed the least.
Lead researcher Professor Seif Shaheen, from Queen Mary, University of London, said: “We cannot say on the basis of these observations that a high intake of sugar by mothers in pregnancy is definitely causing allergy and allergic asthma in their offspring.
“However, given the extremely high consumption of sugar in the West, we will certainly be investigating this hypothesis further with some urgency.
“The first step is to see whether we can replicate these findings in a different cohort of mothers and children.
“If we can, then we will design a trial to test whether we can prevent childhood allergy and allergic asthma by reducing the consumption of sugar by mothers during pregnancy.
“In the meantime, we would recommend that pregnant women follow current guidelines and avoid excessive sugar consumption.”
The study, published in the European Respiratory Journal, drew on data from the Avon Longitudinal Study of Parents and Children.
Also known as the “Children of the 90s” study, the investigation has followed the progress of children whose mothers were pregnant in the early 1990s.
The sugar link with asthma may be explained by high intakes of fructose triggering an immune response leading to inflammation in developing lungs, scientists said.
Fructose is a type of sugar found in fruit, fruit juice and corn syrup and widely used in processed food.
Freely consumed sugar in early childhood had no effect on the results, researchers said. It was foetal sugar exposure that was important.