Authors develop the concept of immunity tolerance and its importance in thyroiditis occurrence and evolution during pregnancy as well post-partum pathology. They also refer the mechanisms that can induce to change the immunity response during pregnancy involving maternal, placental and fetal cytochemistry. It is also proposed a constant and precocious screening of the thyroid dysfunction in pregnant woman with thyroid antibodies, because their positivity prevalence is extremely high as far as the associated risk of abortion.