Hashimoto's thyroiditis (HT), the most prevalent autoimmune thyroid disorder in reproductive-age women, has been linked to diminished ovarian reserve and subfertility. This study aimed to evaluate the relationship between HT and key fertility parameters, including hormonal markers and reproductive outcomes, while also exploring the potential impact of thyroid hormone replacement therapy. A retrospective observational study was conducted on 86 women undergoing fertility evaluation. Participants were divided into two groups based on anti-thyroid peroxidase antibodies (ATPO): the HT group (n = 49) and the control group (n = 37). Among women with HT, 57% were receiving levothyroxine (Euthyrox) at the time of assessment. Variables analyzed included serum levels of anti-Müllerian hormone (AMH), thyroid-stimulating hormone (TSH), insulin resistance index (HOMA-IR), number of oocytes retrieved, blastocysts formed, pregnancies achieved, and live births. Statistical methods included -tests, Mann-Whitney U tests, Pearson/Spearman correlations, and linear regression models. Women in the HT group had slightly lower AMH levels and oocyte counts compared to controls, though these differences did not reach statistical significance. TSH values were higher in the HT group and showed a significant negative correlation with blastocyst formation ( = 0.03). Although TSH also showed negative trends with oocyte count, pregnancies, and live births, these correlations did not reach statistical significance. A post-hoc subgroup analysis revealed that HT patients receiving levothyroxine tended to have higher numbers of oocytes retrieved and blastocysts formed compared to untreated HT patients, suggesting a possible beneficial effect of thyroid hormone replacement, although the differences were not statistically significant. HT is associated with subtle but clinically relevant impairments in ovarian reserve and reproductive potential. Thyroid hormone replacement may offer modest benefits and should be considered in the individualized management of fertility in women with thyroid autoimmunity.