THE EFFECT OF CRYOPRESERVATION IN PREVENTION OF OVARIAN HYPERSTIMULATION SYNDROME

Objective To evaluate the effect of elective cryopreservation of all e mbryos in the prevention of severe ovarian hyperstimulation syndrome i n women at increased risk, following superovulation for in vitro ferti lisation. Design Three hundred and ninety women undergoing superovulat ion for in vitro fertilisation between September 1991 and December 199 2. Setting University Infertility Clinic, Helsinki, Finland. Intervent ions Twenty-three women were considered to have an increased risk of d eveloping ovarian hyperstimulation syndrome. They were characterised b y more than 20 retrieved oocytes and/or by serum oestradiol levels exc eeding 10000 pmol/l on the day of administration of human chorionic go nadotrophin. Instead of cancelling the cycle the oocytes were harveste d and fertilised, and all good quality embryos were cryopreserved. The embryos were thawed and replaced during subsequent natural cycles. Ma in outcome measures Occurrence of ovarian hyperstimulation syndrome an d 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 earl y pregnancy. Among the 23 patients at increased risk there have been 1 5 clinical pregnancies after transfer of two to three frozen-thawed em bryos in natural cycles, with a 32.6% pregnancy rate. Conclusions With holding embryo replacement and elective cryopreservation of the embryo s is effective in preventing severe ovarian hyperstimulation syndrome. After subsequent replacement in natural cycles the implantation rate per embryo is good (22.7%).