Distinction between early and late ovarian hyperstimulation syndrome

To compare patient and cycle characteristics among three study groups: early ovarian hyperstimulation syndrome (OHSS), late OHSS, and non-OHSS.Prospective observational study.University assisted conception service.Women undergoing in vitro fertilization, intracytoplasmic sperm injection or gamete intrafallopian transfer treatment at Bristol University In Vitro Fertilization Service between January 1, 1995, and December 31, 1998.None.Patient age, prevalence of polycystic ovaries, gonadotropin requirement, peak serum estradiol (E(2)) concentration, number of oocytes retrieved, clinical pregnancy rate, number of gestation sacs, and severity of OHSS.Women with early OHSS had significantly higher serum E(2) levels and lower gonadotropin requirements than did the other groups. Cycles with either early or late OHSS had significantly more oocytes collected than those without OHSS. Serum E(2) and oocyte numbers did not accurately predict the risk of developing late OHSS. Clinical pregnancies occurred in all cycles with late OHSS, and multiple pregnancies were significantly more frequent in the late OHSS group than in the other groups. Late OHSS was more likely than early OHSS to be severe.Early OHSS relates to "excessive" preovulatory response to stimulation, whereas late OHSS depends on the occurrence of pregnancy, is likelier to be severe, and is only poorly related to preovulatory events.