Background
Ovarian hyperstimulation syndrome (OHSS) is a complication of in vitro fertilisation (IVF) treatment associated with significant morbidity and mortality.

Aims
To assess the severity of OHSS in patients admitted to a tertiary hospital in Melbourne, Australia, and identify risk factors for the condition.

Material and methods
The files of patients admitted with OHSS over a five‐year period between 2008 and 2013 were reviewed. Baseline characteristics of OHSS patients were compared with IVF patients who did not develop OHSS to establish risk factors for the OHSS patient group. Relative risk was estimated using multivariate Poisson regression. A risk score was then developed using the coefficients from the Poisson regression to aid identification of patients at high risk for the condition.

Results
The following risk factors were associated with an increased risk of developing OHSS: younger age, higher oestradiol (E2) concentration (relative risk (RR) 1.43, P < 0.001), and higher follicle count (RR 1.40, P < 0.001). Lower body mass index (BMI) was not correlated with an increased risk of developing OHSS (RR 1.1, P = 0.19). Conclusions This study demonstrates that a risk score can be calculated from routinely taken measurements to identify patients at high risk of OHSS. Using this risk score could help clinicians reduce the incidence of OHSS by employing preventative strategies in high‐risk patients.