Objective: To investigate whether adding estrogen for luteal support on pregnancy outcomes of fresh embryo transfer cycles using clomiphene citrate (CC) minimal-stimulation protocol in individuals with diminished ovarian reserve. Methods: A retrospective analysis was conducted on the pregnancy outcomes of CC minimal-stimulation protocol for fresh embryo transfer cycles at the Reproductive Medicine Center of the First Affiliated Hospital of Nanjing Medical University from January 2018 to December 2024. A total of 1 778 cycles were included, with adding or not adding estrogen luteal support. Baseline characteristics and pregnancy outcomes were compared between the two groups. Univariate and multivariate retrospective analyses were performed to identify factors influencing clinical pregnancy in the CC minimal-stimulation protocol for fresh embryo transfer cycles. The optimal cutoff value for the receiver operating characteristic (ROC) curve was calculated, and subgroup analysis was conducted based on this value. Results: 826 cases were adding estrogen group and 952 cases were not adding estrogen group. There were no significant differences in baseline characteristics such as female age, male age, female anti-Müllerian hormone (AMH), fertilization method, total CC dose, human chorionic gonadotropin (hCG) daily estradiol and progesterone levels, number of transferred embryos, and trigger medication between the two groups. The estrogen luteal support group had a slightly lower female body mass index (BMI) (P=0.002), lower luteinizing hormone (LH) levels on hCG day (P < 0.001), thinner endometrium on hCG day (P < 0.001), and a higher proportion of transferred blastocysts (P < 0.001). However, there were no statistically significant differences in pregnancy outcomes between the two groups. Logistic regression analysis of factors related to clinical pregnancy showed that female age and endometrial thickness on hCG day were independent influencing factors. The older the female age, the lower the clinical pregnancy rate, and the thicker the endometrium on hCG day, the higher the clinical pregnancy rate. The optimal cutoff value for endometrial thickness was determined to be 7.15 mm based on the area under the ROC curve. In the subgroup of patients with endometrial thickness of 7.2 mm or above on hCG day, the estrogen addition group had higher rate of embryo implantation rate (P=0.015) and live birth rate (P=0.038) compared to the group without estrogen addition group. Conclusions: Using CC minimal-stimulation protocol for fresh embryo transfer cycles in individuals with diminished ovarian reserve, adding estrogen to luteal support in patients with endometrial thickness of 7.2 mm or more on hCG day may lead to better pregnancy outcomes.