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 Thursday, 19 August, 1999, 10:35 GMT 11:35 UK
Mother's hormone levels 'can affect baby's IQ'
Babies could be affected if their mother has an underactive thyroid gland
Pregnant women should be routinely tested for an underactive thyroid since it can lower their child's IQ, according to US research.

A study found that children whose mothers had an untreated underactive thyroid gland when they were pregnant had an IQ which was four points lower than average.

In some cases, the difference was as much as seven points.

None of the children themselves showed signs of the condition at birth.

The thyroid gland secretes hormones which control metabolism, growth and development.

Symptoms can include tiredness, dry skin and weight gain.

Children born with an underactive thyroid gland can suffer learning difficulties.

Pregnant women with the condition are more prone to a potentially life-threatening condition called pre-eclampsia and to have their babies prematurely.

Because foetuses' thyroid glands do not kick into action until the middle trimester of pregnancy, they are reliant on their mother in the early stages.

The researchers from the Foundation for Blood Research in Scarborough, Maine, say even when pregnant women have a mildly underactive thyroid gland and show no symptoms, IQ can be affected.

Their study is published in the New England Journal of Medicine.


The researchers, led by Dr James Hadow, studied children aged seven to nine and compared those born to 124 women with a normal thyroid gland with children born to 62 women with an underactive gland.

Some 19% of the children whose mothers had an underactive thyroid had IQs of 85 or lower.

The average IQ is 100.

Foetuses rely entirely on their mothers' hormones in the early stages of pregnancy
The researchers say: "Hypothyroidism in pregnant women can adversely affect their child's subsequent performance on neuropsychological tests.

"Systematic screening for hypothyroidism early in pregnancy may be worthwhile, even when the degree of deficiency is mild and does not cause immediate clinical manifestations in the woman."

However, in an accompanying editorial, Dr Robert Utiger says that, before screening is proposed, it would be better to encourage manufacturers to add more iodine to foods such as salt and to all vitamin supplements.

Iodine is vital for the production of thyroid hormones.

Intake has declined in some western countries in recent years because people are worried about too much salt in their diet and because manufacturers have reduced the amount of iodine added to bread and animal feed.

"The beneficiaries would be not only pregnant women and their offspring, but everyone," says Dr Utiger.

Some 17.5% of British women are estimated to suffer from hypothyroidism, which is treatable.

It is generally caused by a chronic autoimmune disorder, radioactive iodine therapy, surgery or age-related changes to the thyroid gland.

Diet, ethnicity and geography are also thought to play a big part in the disorder.

For example, in many developing countries, iodine deficiency is endemic.

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