Does subclinical hypothyroidism really affect pediatric IQ?

Apparently not. In a FASTER-related study, researchers from seven centers who studied more than 10,000 patients concluded that the association between subclinical hypothyroidism and lower pediatric IQ does not appear to result from obstetric factors. The finding is of special note given controversy on this question raised by recent studies.

Studying patients enrolled in the FASTER Trial, investigators evaluated whether there's an association between subclinical hypothyroidism or antithyroid antibodies and adverse obstetric outcomes.

Blood tests were performed on the 10,990 patients for thyroid stimulating hormone (TSH), free thyroxine (FT4), antithyroglobulin antibody (antiTG), and antithyroid peroxidase antibody (antiTPO). Defining subclinical hypothyroidism as high TSH with normal-low FT4 or normal TSH with low FT4 and comparing patients to healthy controls, the researchers evaluated pregnancy and pediatric outcomes and confounding factors. They also compared patients with antiTG and/or antiTPO to those without these antibodies.

Cleary-Goldman J, Malone FD, Messerlian G, et al. Subclinical hypothyroidism and pregnancy outcomes. Am J Obstet Gynecol. 2005;193(6 suppl):S20. (Abstract 6).