Symposium: Update on prediction and management of OHSS. Epidemiology of OHSS.

Ovarian hyperstimulation syndrome (OHSS) is a rare iatrogenic complication of ovarian stimulation occurring during the luteal phase or during early pregnancy. The prevalence of the severe form of OHSS is very low and precise analysis of this risk population is difficult. This work reviews the literature in order to identify patients at risk. Data pertaining to the epidemiology and the risk factors of OHSS in women were sought using Medline, Current Contents and PubMed. Relevant papers are summarized. After analysing the data concerning the incidence of OHSS, the pretreatment characteristics of patients were reviewed: age, body mass index, allergies, blood group and aetiology of sterility. The risk factors identified through the ovarian response to stimulation were also analysed: follicular development, oestradiol concentration and other ovarian products. In conclusion, polycystic ovary syndrome may be considered to be a risk factor for OHSS with an evidence level II. However, for other risk factors, only evidence level III could be reached. According to this lack of evidence-based data for predictive factors, all patients are to be considered as potentially at risk for OHSS and treated following to the primum non nocere principle.