Relation of severity of maternal hypothyroidism to cognitive development of offspring

Background-An association between maternal subclinical hypothyroidism and l ow intelligence quotient (IQ) in the offspring has recently been shown. Objective-To provide evidence for the causality of the association by testi ng the hypothesis that severity of maternal hypothyroidism correlates inver sely with IQ of the offspring. Methods-IQ scores were compared among 8 year old offspring of 124 control m others whose thyroid stimulating hormone (TSH) concentrations were < 98th p ercentile of a cohort of 25 000 mothers at 17 weeks gestation, of 28 untrea ted hypothyroid women whose TSH was between the 98th and 99.85th percentile s, and of 20 untreated women whose TSH concentration was greater than or eq ual to 99.85th percentile. Results-Mean (SD) IQs for each group of children tin ascending order of mat ernal TSH concentration) were 107 (13), 102 (15), and 97 (14). The differen ce between the extremes was significant (p = 0.003). The percentage of chil dren with IQs > 1 SD below the control mean was 15, 21, and 50 respectively (p = 0.003). The odds ratio of having an IQ > 1 SD below the control mean, after controlling for socioeconomic status, was 4.7 (p = 0.006) for the th ird group compared with the controls. Conclusions-The inverse correlation between severity of maternal hypothyroi dism and IQ of the offspring supports a causal relation and makes the need to screen for and treat pregnant women for hypothyroidism even more compell ing.