Ovarian hyperstimulation syndrome: definition, incidence, and classification.

Ovarian hyperstimulation syndrome (OHSS) is a iatrogenic complication of controlled ovarian stimulation. Although considered uncommon, the severe form is potentially fatal. Different clinical classifications have been developed through the years. No matter whether it is termed "grade C" or "critical" OHSS, life-threatening events may develop. Hence it is prudent to recognize the population at risk. Several risk factors for OHSS have been identified; some are considered major risk factors such as polycystic ovary syndrome; others are less well defined. Preventive measures could be taken before and during the treatment cycle while taking into consideration the patient's characteristics and the various treatment options and approaches that currently exist.