Maternal thyroid dysfunction during first trimester does not impair child IQ
Maternal thyroid dysfunction during early pregnancy is not significantly associated with poor educational attainment or performance at school in children, according to a recent study.
There was no robust evidence of clinically meaningful associations of first trimester free thyroxine and thyroid stimulating hormone levels with entry stage assessment score or Standard Assessment Test scores at any of the key stages. [BMJ 2018;360:k452]
Associations between maternal free thyroxine or thyroid stimulating hormone and the total number of General Certificates of Secondary Education (GCSEs) passed (range, 0–16) were all close to the null (free thyroxine: rate ratio per pmol/L, 1.00; 95 percent CI, 1.00–1.01; thyroid stimulating hormone: rate ratio, 0.98; 0.94–1.02).
There was still no significant correlation even after more detailed capped scores of GCSEs allowing for both the number and grade of pass or when language, mathematics, and science performance were examined individually, or after all educational assessments undertaken by an individual from school entry to leaving were considered.
A total of 200 (4.3 percent) mothers were newly diagnosed as having hypothyroidism or subclinical hypothyroidism and 97 (2.1 percent) subclinical hyperthyroidism or hyperthyroidism. Children of mothers with thyroid dysfunction and those of mothers with euthyroidism had equivalent number of GCSEs and equivalent grades.
“In this prospective longitudinal study, we did not observe association of maternal first trimester thyroid function with long term educational attainment or on any of the preceding school performance assessment stages,” researchers said.
In some animal studies, maternal hypothyroxinaemia in the first half of pregnancy has been shown to modify neurogenesis and result in neuronal migration errors in the developing brain. [Endocr Rev 1997;18:462-475]
Observational studies examining the effect of low antenatal maternal free thyroxine concentrations on childhood cognitive functioning had variable size (range, 220–5,049) and showed inconsistent results. [Lancet Diabetes Endocrinol 2015;doi:10.1016/S2213-8587(15)00327-7; Thyroid 2015;25:1363-1374; Clin Endocrinol (Oxf) 1999;50:149-155; J Clin Endocrinol Metab 2009;94:497-503; J Clin Endocrinol Metab 2010;95:4227-4234; Epidemiology 2013;24:150-157; J Thyroid Res 2011;2011:426427]
In a recent study involving 3,839 children, there was an inverted U-shaped association between maternal free thyroxine and intelligence quotient (IQ) at age 6 years, with low and high free thyroxine correlated with 1.4–3.8-point reduction in child IQ. [Lancet Diabetes Endocrinol 2015;doi:10.1016/S2213-8587(15)00327-7]
“Conversely, other studies with longer follow up have not found an association between maternal hypothyroxinaemia and cognitive outcomes on repeat assessments at 6 months and 3 years (n=500), or at 6, 12, 24 and 60 months (n=287). [J Clin Endocrinol Metab 2009;94:497-503; J Thyroid Res 2011;2011:426427]
The current study included 4,615 mother-child pairs with an available first trimester sample (median, 10 weeks gestation; interquartile range, 8–12). The main outcome measures were five age-specific national curriculum evaluations in 3,580 children at entry stage assessment at 54 months, increasing up to 4,461 children at their final school assessment at age 15 years.