Maternal Iodine Status, Thyroid Function during Pregnancy, and Child Neurodevelopment

Thyroid hormone regulates the brain development of the fetus. The fetus does not have a mature thyroid gland until mid-pregnancy and is dependent on the transfer of thyroid hormone via the placenta. Adequate maternal thyroid hormone concentrations are therefore essential for an optimal development of the fetal brain. Sufficient iodine intake is also important because iodine is a component of thyroid hormone.

This dissertation investigated which factors determine the iodine status (i.e., urinary iodine concentration) of pregnant women, how iodine status is associated with thyroid function during pregnancy, and how maternal iodine status and thyroid function during pregnancy are related to the IQ score, the risk of ADHD, and autistic traits of the child. This was investigated by means of prospective cohort research.

Besides that we identified country specific dietary determinants, younger (pregnant) women, with a higher BMI and a low intake of dairy products had a greater risk of a lower iodine status. Lower iodine status was associated with only small differences in thyroid function (i.e., higher total thyroxine and a lower thyroid stimulating hormone concentration). Women with an adequate iodine intake had the lowest risk of thyroid autoantibody positivity. A lower iodine status in the first 14 weeks of pregnancy and a low concentration of free thyroxine were associated with a lower IQ score. Maternal iodine status was not associated with ADHD or autistic traits. A low and a high free thyroxine concentration were associated with a higher risk of autistic traits, but firm conclusions could not be drawn. There was no consistent evidence for an association between maternal thyroid function during pregnancy and child ADHD.