Predictive value of serum oestradiol concentrations and oocyte number in severe ovarian hyperstimulation syndrome.

Ovarian hyperstimulation syndrome (OHSS) is a serious complication of gonadotrophin usage but it is difficult to accurately predict its occurrence. Previous investigators have identified the combination of high oestradiol concentrations and oocyte number as being predictive in 80% of cases. In this study we sought to identify the incidence of severe OHSS in patients with high oestradiol concentrations and large numbers of oocytes and to evaluate the importance of pregnancy in the development of OHSS. Between 1990 and 1993, we studied 139 cycles using two assisted reproductive techniques [oocyte donor, n = 72; in-vitro fertilization (IVF), n = 67] in which either oestradiol (> 4000 pg/ml), oocyte number (> 25), or both were elevated. OHSS was diagnosed by standard criteria. There were no cases of severe OHSS in the oocyte donor group and six in the IVF group. Among 10 patients with oestradiol concentration > 6000 pg/ml and > 30 oocytes, only one had OHSS (10%). The relative risk of OHSS with pregnancy was 12 (confidence interval 2.18-66.14). We conclude that the risk of OHSS even at high levels of stimulation is lower than previously believed. Secondly, donors have a very low risk of OHSS, probably because of the absence of pregnancy. As such, cryopreservation of all oocytes in IVF cycles is a reasonable alternative to cycle cancellation or use of adjunctive medication.