**6. Thyroid disorders in pregnancy**

During pregnancy, human chorionic gonodotrophin is produced from placenta. This is structurally similar to TSH. Hence, this stimulates thyroid gland, leading to increase in T4 and T3 and decrease in TSH. Thyroid binding globulin is increased due to estrogen and in turn binds T4 and increases T4 level and increases T4 to T3 conversion. There is increased iodine consumption and increased renal iodine clearance. There is increase of iodine transfer to fetus.
