OBJECTIVE:In this study, we aimed to investigate the prevalence of thyroid dysfunction in pregnant women in their third trimester and assess its relationship with perinatal outcomes.METHODS:A total of 796 women who delivered babies at the Haydarpaşa Numune Training and Research Hospital between January 2014 and January 2015 were evaluated retrospectively. Women with complete data and relevant results from thyroid functions tests were included in the study (n=573). Serum levels of thyroid stimulating hormone (TSH), free triiodothyronine (T3), free thyroxine (T4) were studied for all patients. Patients were classified according to thyroid function test results as having hypothyroidism, subclinical hypothyroidism, hyperthyroidism, or euthyroid state. The perinatal outcomes (Apgar score, birth type and birth weight) were compared.RESULTS:A total of 86.7% of pregnant woman (492/573) showed normal thyroid function tests. Out of the remaining participants,0.5% had hypothyroidism, 8.9% had subclinical hypothyroidism, and 2.8% had hyperthyroidism. TSH levels correlated with maternal age. The perinatal outcomes were insignificant between groups.CONCLUSION:The prevalence of thyroid dysfunction was 13.2% in our population. Subclinical hypothyroidism and hyperthyroidism had no adverse effects on birth weight, cesarean section rates, and Apgar scores.