Hypothyroxinemia alone, also known as low T4emia, is defined as a condition in which a pregnant woman is negative for thyroid autoantibodies, has normal serum thyroid-stimulating hormone levels, and has thyroxine levels below the lower limit of the pregnancy-specific reference range. Recent studies have shown that maternal hypothyroxinemia alone can increase the risk of offspring with reduced IQ, language delay, hypokinesia, autism, and attention-deficit/hyperactivity disorder. It is recommended that patients with hypothyroxinemia simplex in pregnancy should go to regular hospitals and follow the doctor’s instructions for standardized treatment, so as to avoid delaying the condition, which may cause serious consequences to the fetus or the mother.