This study was based on the pathophysiology of the disease and aimed at predicting ovarian hyperstimulation syndrome (OHSS) by determining the importance of ratios obtained from the inflammatory process associated with oestradiol and progesterone in recent years. Out of 242 infertile women who underwent assisted reproductive therapy, 59 patients who developed OHSS were taken as the study group, while the remaining 122 normo-responder (NR) and 61 hyper-responder (HR) patients constituted the control group. The neutrophil to lymphocyte (NLR) and oestradiol/progesterone (EPR) ratios were found to be statistically significantly higher in the OHSS group (P < 0.001). A multivariate logistic regression analysis revealed that the NLR (OR = 2.410, P = 0.001) and EPR (OR = 1.701, P = 0.028) were independent predictors for the development of OHSS. In conclusion, in OHSS inadequate progesterone levels may inhibit suppression of the exaggerated inflammatory process caused by high E2 levels, and NLR and EPR can be used to predict the development of OHSS in patients undergoing controlled ovarian hyperstimulation during in vitro fertilisation cycles.