Purpose To reveal the prevalence of subclinical and overt hypothyroidism among Turkish population during pregnancy. Also to investigate the prevalence of hypothyroidism using ATA 2017 criteria. Methods This is a cross-sectional study. Patients were consisted of 1416 consecutive pregnant women who were universally screened for thyroid disease in their first trimester between 2013 and 2015. Thyroid-stimulating hormone (TSH) and free T4 (FT4) levels were analyzed during the first antenatal visit (before 12 weeks of gestation). We compared different cutoffs for TSH. We further determined the 2.5th and 97.5th percentiles for TSH and FT4. Results Initially, the cutoff of 2.5 IU/ml was selected. Accordingly, 305 women (22.3%) had subclinical hypothyroidism and 22 (1.6%) was diagnosed with overt hypothyroidism. When the cutoff was increased to 4 IU/ml, only 40 (2.9%) women were diagnosed with hypothyroidism. Prevalences of overt hypothyroidism and subclinical hypothyroidism were 0.6% and 2.3%, respectively. Conclusion Universal screening of pregnant women with TSH, using the 2.5 mIU/L cutoff; one in four women was found to be a candidate for thyroid hormone replacement in our cohort. When the cutoff was determined to be 4 mIU/L, prevalence of hypothyroidism decreased approximately 10 times.