Association between thyroidian disease and pregnancy is a frequent event. Thyroidian hormones are mandatory for foetal development especially at the level of brain structures. Any shortage of thyroidian hormone can severely and irreversibly alter neurological development. On the other hand it is also clear that an excess of thyroidian hormone can jeopardize the embryo then the foetus. In case of maternal hyperthyroidism, strict guidelines relying mainly on foetal thyroid monitoring echographic scanning will allow in most cases the delivery of a healthy euthyroid newborn. Hypothyroidia, providing an adequate substitution, has no significant impact on pregnancy. Biological monitoring is the key of monitoring. Iodine deficiency is a matter of concern when considering neurodevelopmental outcome, however it is still an unsolved issue in France. A multidisciplinary team will sometimes be necessary for taking care of pregnant patients with active Graves' disease.