In case of maternal hypothyroidism, the number of miscarriages is higher and reaches 50% in this multicenter study. Several hypotheses are advocated in order to explain this frequent occurrence: the most remarkable is that as substitute treatment is very effective and decreases noticeably the risk of abortion. In case of maternal hypothyroidism, the frequency of abortions in this study reaches 35% before the disease is diagnosed and this figure is not modified (35%) after the diagnosis is made and the treatment initiated. Finally, in case of goiter or euthyroid nodules, there is also a relatively high number of spontaneous abortions. Therefore, there are still a number of unknown factors regarding the role of dysthyroidisms in spontaneous first-trimester abortions.