Ovarian hyperstimulation syndrome: classifications and critical analysis of preventive measures.

The aim of this review was to summarize previously published classifications for ovarian hyperstimulation syndrome (OHSS), as well as to analyse the available methods for preventing OHSS. Withholding hCG and cycle cancellation--once the main methods of preventing OHSS--are now seldom used. There is a growing body of evidence to support the use of coasting to prevent OHSS, without cycle cancellation. However, most studies on coasting are retrospective, and well-designed prospective randomized studies are lacking. There is no current consensus as to how coasting should be carried out. A serum estradiol level of 3000 pg/ml is generally considered optimum for administration of hCG. It appears that intravenous albumin or hydroxyethyl starch at the time of oocyte retrieval is beneficial in preventing OHSS, but does not offer complete protection. There is insufficient evidence to support routine cryopreservation of all embryos for the later transfer of frozen-thawed embryos in high-risk patients. Several uncontrolled studies have reported the protective effect of GnRH agonist to trigger ovulation in preventing OHSS, though the method is applicable solely for gonadotrophin-only or GnRH antagonist cycles. A single dose of recombinant LH to trigger ovulation significantly reduced OHSS as compared with hCG. The possible role of GnRH antagonist protocols in reducing the incidence of OHSS is debatable. The above measures to prevent OHSS were successful in reducing the incidence of the syndrome, but complete prevention is not as yet possible.