High thyroid hormone level will affect fetal brain and neurological development and intellectual development, mainly in the following two cases: 1. High thyroid hormone with decreased FT3 and FT4 levels is called clinical hypothyroidism, and the effect of high thyroid hormone during pregnancy on fetal brain and neurological and intellectual development is more certain; 2. Elevated thyroid hormone but no decrease in T3 and T4 is called subclinical hypothyroidism, and most of the current research results believe that the combination of subclinical hypothyroidism during pregnancy has a certain effect on fetal brain and neurological and intellectual development.