Introduction: Autoimmune thyroid diseases are common findings in women of childbearing age that could affect fertility rate, pregnancy outcome and complications after pregnancy. These diseases also correlated with other autoimmune diseases. Objectives: In this study, we aim to evaluate the autoimmune thyroid disease in women aged 35 to 45 years based on Azar cohort study data. Patients and Methods: In this cross-sectional analytical study, 507 women 35-45 years old without previous thyroid disease from Azar cohort study were evaluated. Demographic findings, data related to previous pregnancies, abortion, miscarriage, infertility and gestational diabetes were recorded for all patients. Blood samples were taken from all patients to measure TSH and anti-thyroid peroxidase (anti-TPO) levels. Anti-TPO levels ≥40 IU/mL were considered positive. Results: In the studied women, miscarriage occurred in 5.3%, abortion in 27.6% and infertility in 7.3%. Gestational diabetes was reported in 3.9%. The positive anti-TPO prevalence was 21.5%. Patients with positive anti-TPO compared to those with negative anti-TPO had significantly higher cases of hypothyroidism (P<0.001). There was no difference between patients with and without positive anti-TPO regarding miscarriage (5% versus 6.4%), abortion (27.4% versus 28.4%), infertility (7.5% versus 6.4%) and gestational diabetes (7.9% versus 3.6%) (P>0.05). There was no correlation between age and anti-TPO levels. Conclusion: The prevalence of thyroid antibodies in our study population is higher than previous studies. Anti-TPO positivity has no significant effect on pregnancy outcome in this population. Further studies are necessary to define the exact effect of anti-TPO on pregnancy outcomes.