Background: In this study, an attempt was made to validate the use of OSI as a measure of ovarian response during IVF treatment and to correlate OSI with age and BMI and other measures of ovarian response such as AMH, antral follicle count (AFC), total dose of administered gonadotrophins, and duration of stimulation. Methods: This study was a retrospective comparative cohort one. The study included a total of 2150 women who underwent the first IVF cycle between January 2008 and December 2017 at our center using long-agonist protocol. Patients were divided into four subgroups according to the circulating AMH level: below the 25th percentile (AMH 0.25-1.1 ng/ml, subgroup A), between 25th and 50th percentiles (AMH 1.2-1.6 ng/ml, subgroup B), between the 50th and 75th percentiles (AMH1.7-2.6 ng/ml, subgroup C), and above the 75th percentile (AMH 2.7-8.5 ng/ml, subgroup D). Qualitative data were analyzed by Chi-square or Fisher’s exact test. The p<0.05 was considered statistically significant. Results: The four subgroups formed on the basis of the AMH level did not significantly differ for age, BMI and infertility duration. OSI was significantly correlated to age (r=0.167; p=0.001), and has negative correlation with AFC (r=-0.236, p=0.001) and AMH levels (r=-0.123, p=0.001). Multiple linear regression analysis was done on OSI with other independent variables such as age, BMI, AFC, AMH. Analysis showed that approximately 8% variation in the value of OSI can be attributed to these variables with the highest correlation with antral follicle count. Conclusion: The present study showed that OSI appears to be a highly reliable index of ovarian responsiveness to recombinant FSH and can be useful to estimate the FSH dose.