The effect of cryopreservation in prevention of ovarian hyperstimulation syndrome

ABSTRACTObjective To evaluate the effect of elective cryopreservation of all embryos in the prevention of severe ovarian hyperstimulation syndrome in women at increased risk, following superovula‐tion for in vitro fertilisation.Design Three hundred and ninety women undergoing superovulation for in vitro fertilisation between September 1991 and December 1992.Setting University Infertility Clinic, Helsinki, Finland.Interventions Twenty‐three women were considered to have an increased risk of developing ovarian hyperstimulation syndrome. They were characterised by more than 20 retrieved oocytes and/or by serum oestradiol levels exceeding 10000 pmol/l on the day of administration of human chorionic gonadotrophin. Instead of cancelling the cycle the oocytes were harvested and fertilised, and all good quality embryos were cryopreserved. The embryos were thawed and replaced during subsequent natural cycles.Main outcome measures Occurrence of ovarian hyperstimulation syndrome and pregnancy rate.Results One out of the 23 patients at increased risk developed a moderate degree ovarian hyperstimulation syndrome, while the others had only mild symptoms. Two of the remaining 367 women with no risk developed ovarian hyperstimulation syndrome, both during early pregnancy. Among the 23 patients at increased risk there have been 15 clinical pregnancies after transfer of two to three frozen‐thawed embryos in natural cycles, with a 32.6 % pregnancy rate.Conclusions Withholding embryo replacement and elective cryopreservation of the embryos is effective in preventing severe ovarian hyperstimulation syndrome. After subsequent replacement in natural cycles the implantation rate per embryo is good (22.7%).