Purpose <p>The purpose of the study is to evaluate the effects of thyroid function on ovarian reserve in reproductive-aged women attending Barkat Infertility Center and Shahid Rahimi Medical Center, Khorramabad, Lorestan, Iran.</p> Methods/Subjects <p>Descriptive-analytical cross-sectional research was conducted on 318 infertile women of reproductive age from July 2023 to March 2024. Subjects were selected through random sampling, and the inclusion criteria required infertility for more than a year without any anatomical, genetic, or systemic causes. A history of prior ovarian surgery, chemotherapy, radiotherapy, thyroid diseases, polycystic ovary syndrome, and hyperprolactinemia were all exclusion criteria. Data on demographic and clinical data were gathered, and blood samples were tested for thyroid function (TSH, FT4) and ovarian reserve markers (AMH, estradiol, and FSH).</p> Results <p>Among the participants, clinical hypothyroidism and subclinical hypothyroidism were found in 10.4 and 3.8% of cases. A significant relationship was identified between TSH and AMH levels. Increased TSH levels and higher FT4 levels were both significantly associated with decreased ovarian reserve, as indicated by AMH &lt; 1.1 ng/mL. Additionally, there were negative correlations for age and BMI with ovarian reserve and positive correlations for estradiol.</p> Conclusion <p>This study concluded that, among infertile women, a significant inverse relationship between thyroid function and ovarian reserve does exist. Higher TSH and FT4 levels were both associated with low levels of AMH; hence, thyroid dysfunction may impair ovarian function. These findings emphasize how imperative complete thyroid investigations are in infertility investigations. Further research is needed to establish the cause and offer specific treatments regarding thyroid disorders and infertility.</p>