Nancy H. Patterson wrote:
The studies came up with an approximate 4-point difference in IQ in a small population of babies born to “naturally” hypothyroid mothers. The results are interesting, may lead to more research, but were not statistically significant.
Here is the Press Release from the ATA back in August:
PRESS RELEASE
The American Thyroid Association
August 19, 1999
Re: Haddow Study of Maternal Hypothyroidism during Pregnancy and
Subsequent Childhood Neuropsychological Development
Background
Thyroid hormone has long been known to be essential for normal brain
development in the fetus and newborn infant. Furthermore, there is
convincing evidence that maternal thyroid hormone can protect the
developing fetus in situations where fetal thyroid function is abnormal.
For example, infants born with thyroid gland underactivity (so-called
congenital hypothyroidism) develop normally as long as their mother’s
thyroid gland function is normal during pregnancy and thyroid hormone
replacement is promptly and properly administered after birth. In
contrast, when the functions of both the mother’s and fetus’ thyroid glands
are impaired, such as occurs in regions with severe dietary iodine
deficiency, the baby can develop permanent mental retardation.
The Haddow Study
In the study by Haddow and his colleagues published in this week’s New
England Journal of Medicine, maternal hypothyroidism, which was
retrospectively diagnosed and unassociated with any known abnormality of
thyroid function in the child at birth, was found to be associated with a
subsequent IQ deficit of 4 points in these children at the age of 7-9
years. Furthermore, in the children whose mothers’ hypothyroidism had been
untreated, this deficit increased to 7 IQ points.
Since the frequency of maternal hypothyroidism is almost 10 times greater
than congenital hypothyroidism, for which newborn thyroid screening is
already routinely performed, this study raises an important question:
Should thyroid function be routinely evaluated by blood testing in all
pregnant mothers, or even in all women of child-bearing age?
Despite the potential importance of this study, its findings are not
conclusive. The IQ deficit observed in the children of hypothyroid mothers
was small. It is also possible that the observed difference in these
children’s IQ’s could have been due to factors other than the maternal
hypothyroidism.
Recommendations of The American Thyroid Association
The American Thyroid Association believes that this provocative study
should prompt additional research to confirm whether there is a
relationship between maternal thyroid dysfunction during pregnancy and
subsequent neuropsychological development in children. In addition to
further clinical research, decisions regarding routine maternal thyroid
function screening during early pregnancy must take into account the
potential benefits and costs of such screening for mothers, their children,
and society as a whole.
While awaiting the results of further research, The American Thyroid
Association recommends that:
The decision about whether and when to assess thyroid function in a woman
of child-bearing age should be left to the judgments of individual women
and their doctors
Woman of any age with new, persistent, or multiple symptoms of
hypothyroidism (such as unexplained fatigue, intolerance of cold
temperatures, constipation, dry skin, mental slowing, and depression)
should be screened for hypothyroidism
Women with previous thyroid disease or treatment, a family history of
thyroid disease, or enlargement of the thyroid gland (goiter) should be
considered at particularly high risk.
When it is appropriate to evaluate a woman’s thyroid status, the TSH blood
test is recommended as the procedure of choice.
