Thyroid Deficiency in Pregnancy Affects Child IQ
Even a mild, symptom-free case of
thyroid deficiency in a pregnant woman can affect her child's IQ
scores years later, results of a study suggest.
Children aged 7 to 9 who had mothers with untreated hypothyroidism
in pregnancy had IQ scores about 7 points lower than youngsters of
women without such a deficiency, according to study results
published in the August 19th issue of The New England Journal of
The findings suggest that "routine prenatal or pre-pregnancy
screening for thyroid deficiency needs to be considered," said
lead study author Dr. James E. Haddow, of the Foundation for Blood
Research in Scarborough, Maine, in an interview with Reuters Health.
In the report, the researchers note that for the first 12 weeks of
pregnancy, before the unborn child's thyroid becomes active,
"the mother is the sole source of thyroid hormones."
Studies suggest that these hormones play a role in brain
Haddow and colleagues screened stored blood samples from more than
25,000 women who were pregnant between January 1987 and March 1990.
They identified 62 women with thyroid deficiency, of whom 48 were
not treated for hypothyroidism throughout pregnancy.
The investigators tested the neuropsychological development of the
offspring of the 62 women and compared them with the children of 124
women without thyroid problems in pregnancy.
Between ages 7 and 9, children of the 48 mothers with untreated
hypothyroidism scored 7 points lower, on average, on the Wechsler
Intelligence Scale for Children. By comparison, IQ scores were
similar between children of women whose hypothyroidism was treated
during pregnancy and other youngsters.
Overall, compared with other children, the offspring of
thyroid-deficient mothers had impaired school performance and lower
scores on tests of attention, language, and visual-motor
"Eleven years after the pregnancy under study, 64% of the
untreated women and 4% of the matched control women had confirmed
hypothyroidism," the investigators write, based on data from
questionnaires they mailed. On average, hypothyroidism had been
present for about 5 years in these women before being diagnosed,
"What we don't know from this study is whether you can
effectively avoid the IQ problem in the child (by treating the
mother's thyroid deficiency)," he said. However, because of the
"minimal" risk of treating thyroid disease in pregnancy,
the typical long delay in diagnosis and the simplicity of screening
for thyroid deficiency, Haddow believes that widespread screening
for hypothyroidism in pregnant women is "worth
In an editorial, Dr. Robert D. Utiger notes that there are two
potential causes of hypothyroidism in women: chronic autoimmune
thyroiditis and iodine deficiency. He suggests that both causes
likely play a role in thyroid deficiency in the US, where 15% of
women of childbearing age had "overtly inadequate" intake
of iodine between 1988 and 1994.
With this in mind, the editorialist notes that efforts to increase
dietary iodine intake in the US should be the first step in any
program to help prevent the adverse effects of hypothyroidism during
pregnancy. "The beneficiaries would be not only pregnant women
and their offspring, but everyone," Utiger concludes.