Distinction between early and late ovarian hyperstimulation syndrome

Objective: To compare patient and cycle characteristics among three study g roups: early ovarian hyper stimulation syndrome (OHSS), late OHSS, and non- OHSS. Design: Prospective observational study. Setting: University assisted conception service. Patient(s): Women undergoing in vitro fertilization, intracytoplasmic sperm injection or gamete intrafallopian transfer treatment at Bristol Universit y In Vitro Fertilization Service between January 1, 1995, and December 31, 1998. Intervention: None. Main Outcome Measure(s): Patient age, prevalence of polycystic ovaries, gon adotropin requirement, peak serum estradiol (E-2) concentration, number of oocytes retrieved, clinical pregnancy rate, number of gestation sacs, and s everity of OHSS. Result(s): 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 tho se without OHSS. Serum E-2 and oocyte numbers did not accurately predict th e 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. Conclusion(s): Early OHSS relates to "excessive" preovulatory response to s timulation, whereas late OHSS depends on the occurrence of pregnancy, is li kelier to be severe, and is only poorly related to preovulatory events. (Fe rtil Steril(R) 2000;73:901-7. (C) 2000 by American Society for Reproductive Medicine).