Hypothyroxinemia during pregnancy: the effect on neurodevelopment in the child

► A lack of iodine in the diet may result in the mother becoming iodine deficient, and subsequently hypothyroxinaemic. ► Maternal hypothyroxinemia has a detrimental effect on fetal brain development. ► Screening fT4 at 12 weeks could indicate a subgroup of women whose infants would benefit from an increase of maternal fT4. Experimental studies have shown that maternal hypothyroxinemia during early pregnancy is associated with poor neurodevelopment in affected offspring. The aim of this study was to assess the impact of maternal serum free T4 on psychomotor development of offspring. The study involved 147 women in the third trimester (week 37) of pregnancy. TSH and free T4 serum levels were measured at 37 week gestation. The children were evaluated between 38 and 60 months of age by the McCarthy Scales of Children's Abilities. 54.4% of the women had a free T4 below the threshold of hypothyroxinemia. We find a significant effect of maternal hypothyroxinemia on the general cognitive index, and on perceptual-manipulative and memory coefficients.