Obiectives: To assess the prevalence of thyroid dysfunction in a group of pregnant women, originating from Dobrogea region of southeastern Romania, considered to be an area without iodine deficiency, including the Black Sea area. Materials and methods: We enrolled 324 pregnant women in different trimesters of pregnancy. Each case was reviewed by a detailed madical history, clinical examination and by serum dosage of thyroid hormones: TSH, FT4, and the antithyroidperoxidase. They were evaluated by comparison with trimester -specific reference range for TSH recommended by American Thyroid Association, then the results were compared with those obtained using the manufacturers reference range. Abortion rate was also analysed. Results: The prevalence of thyroid dysfunction was different in all the 3 trimesters: subclinical hypothyroidism being the most frequently approx. 24% of all cases; 7% of pregnant women had overt hypothyroidism. Incidence of thyrotoxicosis in entire study cases was approx. 5.5%. The most frecvent thyroid autoimune disorders were Hashimoto thyroiditis: 42 % - I trimester, 26,6% in II trimester and about 12,5 % in III-trimester; Graves disease have an incidence of only 0,9 % (n=3).The difference between reference methods eluded a lower number of cases using manufactures reference range for TSH (P< 0,001), but higher for recommended trimester - specific TSH value, confirming the undervalueted hypothesis. The risk of misclassifying the hypothyroidism is between 3 %-8 %. Conclusion: Necessity for thyroid hormone dosage periodic/trimesterly/ in pregnancy is a preventive measure. The reference values for hormonal dosage requires trimester-specific assessment. The possibility of hormonal disorders during pregnancy is common. The need for specific therapy at diagnosis depends on the nature of hormonal disorder. Further precautions are needed in pregnant women with known autoimmune thyroid disorder or newly diagnosed