Results were published in the October 2011 issue of the journal Thyroid in an article titled “Subclinical hypothyroidism in pregnancy: intellectual development of offspring.”
The study included 44 children between the ages of 4 and 15 years old, born to 44 mothers.
The mothers of these children were part of a sub-pool of 90 women, identified from within a group of 441 women of reproductive age who had hypothyroidism. These women were seen in endocrine clinics during their pregnancy in Tehran, Iran, between 1991 and 2003.
In this study, the mothers were already receiving levothyroxine (LT4) before their pregnancy. Nineteen mothers had normal serum thyrotropin (thyroid-stimulating hormone [TSH]) during pregnancy (the control group).
Mothers of the other 25 children had increased TSH during the comparable pregnancy: Nineteen mothers had M-SCH (the case group), and 6 mothers had overt hypothyroidism.
Three tests were performed (serum TSH, free T4, and urine iodine). In addition to these, 7 cognitive performance and intelligence quotient (IQ) tests were completed.
The research team found that case group children were similar to control group children with respect to:
In the case group, maternal TSH (mean±standard deviation) during pregnancy was 11.3±5.3, and in the control group, maternal TSH was 1.4±1.0 (p<0.001).
For the 2 groups, serum TSH, freeT4, urinary iodine concentrations, and cognitive performance tests were similar. Total IQ (case group: 120±14; control group: 121±11), performance IQ (case group: 117±12; control group: 120±7), and verbal IQ (case group: 121±16; control group: 117±15) were also similar for both groups.
With the exception of education level of the mother and neonatal weight, no relationships were observed between variables and IQ.
Researchers determined that IQ level and cognitive performance of children born to mothers with hypothyroidism who were treated with LT4 were similar in the mothers who had M-SCH during pregnancy compared with the mothers who had normal serum TSH concentrations throughout the pregnancy.