During the last two decades, insights into the pathophysiologic mechanism of maternal and fetal thyroid function during pregnancy have shown that the developing brain is strongly dependent on the thyroid hormone. Fetal thyroid function is totally dependent on maternal supply until 16–20 weeks of gestation, until which time the fetus does not produce the thyroid hormone. The negative impacts of maternal thyroid dysfunction on fetal development during pregnancy — hypothyroidism, Graves disease, endemic iodine deficiency, for example — have long been described. Very recently, several articles have been published about the possible harmful effects of subnormal fluctuations (i.e., generally considered normal or, more specifically, not considered to have negative effects) of maternal thyroid hormone levels during early pregnancy and subsequent impaired development of the offspring. Although an explanation is still lacking, the impact of these findings could be far-reaching: low “normal” maternal thyroid function appears to refer to thyroid hormone levels at or below the 10th percentile, suggesting that a substantial number of apparently healthy pregnant women could be at risk for impaired development of their offspring. Further research is needed to evaluate the consequences of these findings on a population-based level.
*Department of Clinical Health Psychology, University of Tilburg, The Netherlands; †Emma Children’s Hospital, Academic Medical Center, University of Amsterdam
Correspondence to: Victor J. Pop, PhD, MD, Associate Professor, Department of Clinical Health Psychology, University of Tilburg, The Netherlands; e-mail: firstname.lastname@example.org
Thomas Vulsma, MD, PhD, MSc, Pediatric Endocrinologist, Emma Children’s Hospital, Academic Medical Center, University of Amsterdam; e-mail: email@example.com