The link between the growth of a baby in the womb and its likelihood of developing asthma in childhood was found by a team at the University of Aberdeen, who did tests at various stages of pregnancy.
The researchers also found links between the growth rate of unborn children and their chances of developing eczema and hay fever.
The team took foetal measurements of 1,500 pregnant women at Aberdeen Maternity Hospital during their first and second trimesters, at 10 weeks, then at 20 weeks gestation, and followed up with the children when they were aged 10.
A total of 927 families filled in respiratory questionnaires for their child and 449 children underwent lung function and skin prick testing which looked for allergies to grass, eggs, dust mites and cats.
The results showed the children aged five and 10 who had asthma had been 5mm or 10 per cent smaller than average as 10-week-old embryos.
The study revealed that an unborn baby smaller than the average foetus at 10 weeks and which remained small throughout pregnancy was five times more likely to develop childhood asthma.
The results showed that a foetus which started off bigger than average at 10 weeks, but whose growth slowed resulting in them becoming smaller than average at a later stage, were more likely to be protected against hay fever.
Dr Steve Turner, who led the study, is a consultant with NHS Grampian and the clinical senior lecturer at the University of Aberdeen's department of child health.
He said: "Our main finding was that the shortest foetuses in the first trimester were at increased risk for persistent wheeze whereas the longest babies had better lung function at 10 years."