Taking standard iodine supplements during pregnancy can raise iodine levels in urine beyond the safety threshold recommended by the WHO, even in women who are only mildly deficient.

Giving iodine supplements to pregnant women with mild iodine deficiency does not reduce the occurrence of isolated hypothyroxinemia or subclinical hypothyroidism, even when urinary iodine levels rise, suggesting the supplements do not resolve the underlying thyroid hormone imbalance.

In pregnant women with mild iodine deficiency, taking 200 micrograms of iodine daily is linked to a small but measurable reduction in the levels of thyroid hormones called free and total thyroxine during the later stages of pregnancy.

Pregnant women with slightly low iodine levels don’t seem to have noticeable changes in their thyroid hormones compared to those with good iodine levels — their thyroid still works fine even if their iodine isn’t perfect.

For pregnant women with mild iodine deficiency, taking a 200 μg iodine supplement daily does not improve their child's thinking or movement skills by age 5.7, and may be linked to slightly lower motor skills at age 2, suggesting no overall advantage for brain development.