Dr Finken's team measured thyroxine levels in the mothers of 1,196 healthy children when they were 12 weeks pregnant.
After birth, the children's progress was followed until age five, when test scores for language and arithmetic were recorded.
The study found that five-year-olds whose mothers had the lowest levels of thyroxine at the end of their first three months of pregnancy were almost twice as likely to score "subnormal" marks in the maths test.
When influences of family background and health factors were stripped out of the results, a 60 per cent difference in the test scores remained.
A "subnormal" test score was defined as coming in the bottom half of the class.
In the future, hormone tests could conceivably be used to identify children likely to need extra help in maths at school, said the researchers, whose findings appear in the European Journal of Endocrinology.
Dr Finken added: "It is possible that these children could benefit from hormonal supplements to boost their brain development in the womb. Such treatment has been tried in the past but as yet has failed to improve cognitive ability."
- PAA