Objective: To determine the incidence of ovarian hyperstimulation syndrome (OHSS) and subsequent pregnancy rates (PRs) if ET is delayed in patients at risk of OHSS by allocating all embryos to cryopreservation.
Design: Retrospective analysis of clinical and laboratory data from 724 consecutive stimulated cycles of IVF.
Setting: University hospital-based IVF program.
Patients: Consecutive patients undergoing IVF between September 1989 and December 1992.
Main outcome measures: Fertilization rates, cryosurvival rates, subsequent PRs, and the occurrence of severe OHSS.
Results: Ten of the 564 patients (1.8%) who had ET in the stimulation cycle developed severe OHSS. Sixty-nine patients had all embryos frozen because of the risk of OHSS, of which one (1.4%) developed severe OHSS. The subsequent PR after thaw transfer was 25.2% per transfer, with a cumulative PR per patient after additional thaw transfers of 40.6%.
Conclusions: Cryopreservation of all embryos and delayed ET in patients at risk of OHSS results in a low incidence of severe OHSS. Oocyte quality, fertilization rates, and cryosurvival of frozen embryos are equal to those for patients who have a normal stimulation profile. Subsequent thaw embryo replacements result in a satisfactory PR.