Infertility is defined as the inability of a couple to achieve pregnancy within a certain period despite regular sexual intercourse. With technological advances, infertility treatments have also advanced, and assisted reproductive technologies have become increasingly widespread. In this study, the potential interference effects of different gonadotropin preparations used during controlled ovarian stimulation in in vitro fertilization treatment on hormone levels were experimentally investigated. The effects of urine-derived (menotropin and urofollitropin) and recombinant (folitropin and folitropin + lutropin) gonadotropin preparations on the hormone levels were evaluated. Interference effects on follicle-stimulating hormone (FSH), luteinizing hormone (LH), estradiol, progesterone, prolactin, testosterone, thyroid-stimulating hormone, free T3, and free T4 hormone levels were analyzed using immunoassay techniques. The results showed significant deviations, especially in the FSH and LH tests, whereas the interference levels varied among the different preparations. The highest interference was observed in the FSH assays, with deviations reaching up to 292,138%. Significant differences were also observed in estradiol and thyroid hormones (free T3 and free T4). These findings suggest that gonadotropin drugs containing high concentrations of FSH and LH may interfere with routine immunoassay-based hormone tests, leading to errors in clinical interpretation. This study emphasizes the need for careful interpretation of hormone assays in patients undergoing in vitro fertilization treatment, and the importance of considering possible interference effects.