Prenatal thyroid drugs don’t boost kids’ IQ

CARDIFF (UK) — Children of mothers screened and treated for reduced thyroid function during pregnancy show no signs of improved IQ, new research shows.

Scientists took blood samples from more than 20,000 women at about 13-weeks of pregnancy to test for thyroid function who were randomly assigned to one of two groups.

In the first group, women with low thyroid function were given the thyroid hormone levothyroxine to take during the remainder of their pregnancy. In the second group, women with low thyroid function did not receive levothyroxine.


The children of the mothers with low thyroid function were tested by psychologists at the age of three to assess their IQ.

“Previous research indicated an association between low maternal thyroid hormone levels in pregnancy and low IQ in children but it was not known whether early treatment with thyroid hormone could prevent the impairment,” says John Lazarus, professor in the Center for Endocrine and Diabetes Sciences at Cardiff University.

“Our study showed no such preventive effect. There was no difference in IQ between children of women who received thyroid hormones and children of women in the group that didn’t. This indicates that testing for low thyroid function in early pregnancy does not prevent impairment of childhood cognitive function.”

Reported in the New England Journal of Medicine, the study supports current UK guidelines that don’t recommend routine antenatal screening for hypothyroidism in pregnancy.

“Earlier work suggested that as many as one in five children with lower IQs might be attributable to low thyroid status in the mother,” says Nicholas Wald, professor from the Wolfson Institute. This earlier work raised the possibility that antenatal screening would be worthwhile. It is disappointing that the results of our randomized trial showed no benefit.”

Scientists from the Wolfson Institute of Preventive Medicine at Barts and the London School of Medicine and Dentistry, Queen Mary University of London, and colleagues from Turin, Italy, contributed to the research, which was funded by the Wellcome Trust and Compagnia di San Paulo, Turin.

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