Hormone deficiencies in pregnant women may impact on their children's abilities in school later in life, scientists have warned.
A study following almost 1,200 youngsters found that those born to women with low levels of a thyroid hormone were 60 per cent more likely to struggle with maths in the classroom, compared to mothers with normal hormone levels.
Researchers, lead by Dr Martijn Finken, from the VU University Medical Centre in the Netherlands, measured levels of thyroxine in the mothers of 1,196 healthy children when they were 12 weeks pregnant.
The children's progress was monitored as they grew older, and when they hit the age of five they were given language and arithmetic tests.
Those whose mothers had recorded the lowest levels of thyroxine were almost twice as likely to place in the bottom half of results in the maths test - even when factors such as family background and health were stripped out.
Dr Finken said the research suggested there could be a place for hormone tests to determine which children are likely to need extra help in the classroom.
Previous studies had already revealed a link between a lack of the hormone and impaired mental development in very young children, but this was the first study to examine how it may affect children in school.
The findings were published in the European Journal of Endocrinology.