Subclinical hypothyroidism in pregnancy: intellectual development of offspring.

Background: The effects of maternal subclinical hypothyroidism (M-SCH) on the neuropsychological development of the offspring are not clear. We evaluated the intellectual development of children of mothers who had M-SCH during the pregnancy for these children.

Methods: Sixty-two children were recruited. After excluding those age < 4 or age > 15, 44 were enrolled. The mothers of these children were part of a sub-pool of 90, of 441 hypothyroid women of reproductive age seen in Tehran endocrine clinics between 1991 and 2003 and who were observed during gestation. Mothers were receiving levothyroxine (LT4) before gestation. Mothers of 19 children (control group) had normal serum thyrotropin (TSH) during the pregnancy that produced these children. Mothers of the other 25 children had increased TSH during the comparable pregnancy. Nineteen mothers had M-SCH (case group) and six had overt hypothyroidism. Serum TSH and free T4 (FT4) and urine iodine were measured, and seven cognitive performance and intelligence quotient (IQ) tests were performed.

Results: Case children were similar to control children with respect to gender, age, parental education, maternal age at time of pregnancy and at the time of their hypothyroidism, percent mothers having thyroid peroxidase antibodies, LT4 dose of mothers during pregnancy, gestational age at delivery, birth weight, and duration of breast feeding. Maternal TSH (mean ± standard deviation) in the case group during their mother's pregnancies was 11.3 ± 5.3 and 1.4 ± 1.0 mU/L in the controls (p < 0.001). Serum TSH, FT4 and urinary iodine concentrations were similar in the two groups. Total IQ, performance IQ, and verbal IQ were similar, being 120 ± 14, 117 ± 12, and 121 ± 16, respectively, in the case group and 121 ± 11, 120 ± 7, and 117 ± 15 in the control group. Cognitive performance tests were similar in both groups. No relationships were observed between variables and IQ except for education level of the mother and neonatal weight.

Conclusion: IQ level and cognitive performance of children born to LT4-treated hypothyroid mothers is similar in those whose mothers have M-SCH during pregnancy compared with those whose mothers have normal serum TSH concentrations during pregnancy.