ESPE Yearbook of Paediatric Endocrinology

To read the full abstract: BMJ 2018;360:k452

The role of thyroid hormones during early gestation is well established by animal studies. In humans, previous studies have shown that maternal hypothyroxinemia was associated with either an early reduction in psychomotor scales (e.g. Bayley scale of infant development) or later in late infancy or adolescence. However, randomized controlled trials on the effect of antenatal screening and treatment of mild thyroid disorders did not show any difference in cognitive function between children of mothers treated and not treated (see also paper 3.6)^1,2.

The present observational study offers the advantage of a long-term assessment of school performance and education achievement in a large number of UK mother-children pairs. The authors found no significant difference in long-term school performance at any assessment for any thyroid disorder. They concluded that first trimester suboptimal thyroid function is unlikely to have effects on school performance.

The strengths of this important observational study are: 1) comparison of the effect over the whole spectrum of maternal thyroid diseases (subclinical and overt hypothyroidism, isolated hypothyroxinemia and subclinical and overt hyperthyroidism, isolated hyperthyroxinemia) on offspring intellectual development, 2) detection of maternal thyroid disease as early as in the first trimester, when embryonic cerebral development is completely dependent on transplacental transfer of maternal thyroid hormone, 3) evaluation of all children by “real-life” standardized school tests, and 4) re-evaluation of all children 3 times until 15 years of age. Interestingly, there were no expected trends of decreasing school performance with increasing severity of hypo- or hyperthyroidism. Two possible limitations need to be kept in mind: the small sample size with overt hypothyroidism (n=17 with TSH <10 mU/L; n=17 with TSH >10mU/L), and incomplete information on maternal iodine status. Nevertheless, these results are reassuring and important.

1. Lazarus JH, Bestwick JP, Channon S, Paradice R, Maina A, Rees R, Chiusano E, John R, Guaraldo V, George LM, Perona M, Dall’Amico D, Parkes AB, Joomun M, Wald NJ. Antenatal thyroid screening and childhood cognitive function. N Engl J Med 2012; 366:493-501

2. Casey BM, Thom EA, Peaceman AM, Varner MW, Sorokin Y, Hirtz DG, Reddy UM, Wapner RJ, Thorp JM, Jr., Saade G, Tita AT, Rouse DJ, Sibai B, Iams JD, Mercer BM, Tolosa J, Caritis SN, VanDorsten JP, Eunice Kennedy Shriver National Institute of Child H, Human Development Maternal-Fetal Medicine Units N. Treatment of Subclinical Hypothyroidism or Hypothyroxinemia in Pregnancy. N Engl J Med 2017; 376:815-825