Most pregnant women do not know about a common nutritional deficiency which can cause intellectual disability in unborn children, according to new research.

The study, from Glasgow University, estimates nearly three quarters of pregnant women do not get enough iodine in their diet, while 84% were unaware that it is vital for the healthy development of their unborn baby.

Researchers say more advice is needed to ensure expectant mothers and breastfeeding mums know the importance of iodine and how to get it in the diet, and government should consider whether to fortify food with iodine. At present a diet of sea fish and dairy foods is the best way to improve iodine intake and research last July, also published by Glasgow University, suggested eating Scottish seaweed could help tackle iodine deficiencies. A shortage of iodine affects 1.9 billion people globally and is the most preventable cause of intellectual disability, and the UK is ranked 8th in a list of iodine-deficient countries in the world.

The study surveyed 1,026 women across the UK who were pregnant or mothers of children aged up to 36 months. While most were aware of other nutritional needs such as for folic acid and Vitamin D in pregnancy, 84% were unaware that iodine was important and only 11% had been told about it by a health worker. The study found 56% could not identify a single iodine-rich food. The majority wrongly believed table salt and dark green vegetables had high levels.

Iodine is needed to produce thyroid hormones, crucial for fetal development, and studies have shown links between iodine deficiency and developmental impairments.

But only 26% of women surveyed consume the daily minimum 250 microgrammes of iodine advised by the World Health Organisation. However the UK recommendation is lower and makes no distinction for pregnant and breastfeeding women.

Dr Emilie Combet, of Glasgow University, said unborn children and babies were entirely reliant on their mother for iodine supply: "Women aren't receiving the message about the importance of iodine in pregnancy, meaning they cannot make informed choice.

"Iodine is crucial to ensure adequate brain development, but achieving over 200ug a day of iodine through diet requires regular consumption of foods such as milk and sea fish. Not everyone will have the knowledge, means or opportunity to achieve this."

Fortifying salt with iodine is common in other countries, but would conflict with messages telling people to cut down their salt intake. It was reported last month that a rise in consumption of organic milk might be contributing to iodine deficiencies, after a study from Reading University found that it could contain up to a third less iodine than non-organic varieties. However the findings have been disputed by the dairy industry.