Pregnancy has a profound impact on the thyroid gland and thyroid function .During pregnancy the thyroid is hyperstimulated, resulting in changes in thyroid hormone concentrations.

Accurate assessment of thyroid function during pregnancy is critical.Trimester-specific intervals are especially important during pregnancy when thyroid insufficiency may be associated with adverse obstetric outcome and fetal neurodevelopmental deficits.

Knowing the expected normal changes in hormone concentrations throughout pregnancy allows individualized supplementation when necessary.