Aim: The aim of the study is to determine the frequency of first-trimester thyroid dysfunction in pregnant women and to investigate the effect of thyroid dysfunction on some perinatal outcomes. Material and Method: In the study, first-trimester Thyroid stimulating hormone (TSH), free T4 and free T3 hormone values of pregnant women who applied to our outpatient clinic were retrospectively scanned and recorded. As a result, 3224 pregnant women were included in the study. Pregnant women were evaluated as overt hypothyroidism, subclinical hypothyroidism, overt hyperthyroidism, subclinical hyperthyroidism and euthyroid according to TSH and fT4 values. Results of thyroid function tests of pregnant women and some perinatal results (age, gestational week, delivery type, baby gender, birth weight, gravida, parity, abortion) were compared Results: In our study, the mean age of the pregnant women for screening was 28.6±3.1, the mean birth week was 38.7±2.1, and the mean birth weight was 3037±324.73.6% (n=2369) of the pregnant women were normal euthyroid, 0.71% (n=23) were subclinical hyperthyroidism, 0.65% (n=23) were overt hyperthyroidism, while 15.6% (n=507) were overtly hypothyroid and 9.4% 3 (n=304) were found to be subclinical hypothyroidism. A significant statistical difference was not found between thyroid outcome test results and perinatal outcomes (age, gravida, parity, abortion, birth strength, gestational age, delivery type, babies) (p> 0.05). Conclusion: In our study, a high prevalence of thyroid disease, especially hypothyroidism, was observed in pregnant women. More studies should be done to evaluate the effect of thyroid functions on pregnancy outcomes.