Vol. 5, No. 4, 1999 Page 4

Maternal hypothyroidism lowers babies’ IQs

Millions of American women suffer from undiagnosed hypothyroidism, which can cause mental and physical debility. A new study reveals that not only these women, but also their children, may suffer as a result of their missed diagnoses-even if the children do not suffer from hypothyroidism themselves.

J. E. Haddow and colleagues studied stored serum samples collected from pregnant women between 1987 and 1990, and located 62 of the women whose samples identified them as having hypothyroidism. They then compared these women’s children, who were between s seven and nine at the time of the study, to a control group of 124 children born to mothers with normal thyroid function. None of the children in either group were hypothyroid at birth.

Haddow et al. report that the children of the hypothyroid women performed slightly less well on all 15 tests used to measure cognitive functioning, and had IQ scores an average of 4 points lower than control children. Problems were more marked among child dren of the 48 women who received no treatment for their hypothyroidism during pregnancy, with 19 percent having IQs of 85 or less (compared with 5 percent of controls). Low IQ, in addition to being a risk factor for school failure, is a strong risk facto or for delinquency and criminality.

The researchers conclude, “Undiagnosed hypothyroidism in pregnant women may adversely affect their fetuses; therefore, screening for thyroid deficiency during pregnancy may be warranted.”


“Maternal thyroid deficiency during pregnancy and subsequent neuropsychological development of the child,” J. E. Haddow, G. E. Palomaki, W. C. Allan, J. R. Williams, G. J. Knight, J. Gagnon, C. E. O’Heir, M. L. Mitchell, R. J. Hermos, S. E. Waisbren, J. D D. Faix, and R. Z. Klein, New England Journal of Medicine, Vol. 341, No. 8, August 19, 1999, pp. 549-555. Address: J. E. Haddow, Foundation for Blood Research, Scarborough, ME 04074.

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