Introduction

Ovarian stimulation exposes the body to supraphysiological levels of steroid hormones. The most serious complication related to that stimulation is the ovarian hyperstimulation syndrome (OHSS) characterized by the shift of protein-rich fluid from the intravascular space to the third space, mainly the abdominal cavity. Two main clinical forms of OHSS, the early and the late, are distinguished by their time of onset and by the origin of the human chorionic gonadotropin (hCG) triggering that induces this complication. Early OHSS usually occurs within 9 days of oocyte retrieval in response to exogenous hCG, while endogenous hCG of early pregnancy or exogenous hCG for luteal phase support mainly causes the late OHSS.

According to the literature, the incidence of moderate cases of OHSS is about 5%, whereas in 2% (on average) of cycles hospitalization is required [1, 2]. Apart from the physical discomfort, the disorder constitutes a serious health risk and may even be fatal. Reports on maternal mortality rates from the Netherlands and the UK indicate an incidence of about 3 deaths per 100000 cycles performed [3, 4]. In view of the rapid expansion of assisted reproductive treatments, the total number of maternal deaths related to OHSS may be far greater than initially expected [5]. In this chapter, we give an overview of the approaches available to limit or even completely prevent the occurrence of this complication.