Background: Progesterone levels are critical for endometrial receptivity and implantation success in assisted reproductive technology (ART). The purpose of the current study was to determine whether serum progesterone levels on oocyte retrieval day predict pregnancy success in fresh embryo transfers. Methods: This prospective cross-sectional study was conducted at a university-affiliated infertility clinic in Tehran, Iran, in 2024. Blood samples were collected to analyze serum levels of estradiol (E2), progesterone (P4), follicle-stimulating hormone (FSH), luteinizing hormone (LH), and anti-Müllerian hormone (AMH) using standardized methods. Student’s t-test and the Mann-Whitney U test were conducted for primary comparisons. Logistic regression was applied to adjust for covariates. The optimal progesterone cutoff was calculated by receiver operating characteristic (ROC) curve. The level of statistical significance was 0.05. Results: Ninety-one infertile women participated in the study, with a mean age of 35.56±4.45 years and a mean BMI of 25.98±2.2. Among those who under-went fresh embryo transfer (n=63), 21 had positive serum β-hCG results, and fetal heart rate was detected via ultrasound in 17 patients at six weeks. Proges-terone levels were significantly higher in the pregnancy-confirmed group (8.46 ng/ml) in comparison to the non-pregnant group (5.95 ng/ml, p=0.005). Similarly, patients with clinically confirmed pregnancies (detection of fetal heart rate) had significantly higher progesterone levels (8.38 ng/ml) compared to those without clinical pregnancy (6.19 ng/ml, p=0.02). A cutoff of 7.1 ng/ml predicted chemical pregnancy with 76.2% sensitivity and a cutoff of 7.55 ng/ml predicted clinical pregnancy with 71% sensitivity. Conclusion: Elevated serum progesterone levels on the day of oocyte retrieval may predict positive pregnancy outcomes, highlighting the importance of moni-toring progesterone to optimize the success rate of ART.