Optimal follicle and oocyte numbers for cryopreservation of all embryos in IVF cycles at risk of OHSS

Ovarian hyperstimulation syndrome (OHSS) is a rare but potentially fatal complication of IVF treatment. The risk of OHSS increases with increasing numbers of follicles aspirated and oocytes retrieved, but there is little evidence to support whether threshold values of either can be used to correctly predict OHSS. Since the most severe forms of OHSS are usually associated with pregnancy, cryopreservation of all embryos may prevent this. The authors attempted to find thresholds of follicle and oocyte numbers that would optimally predict OHSS, through a retrospective analysis of 2253 consecutive cycles of IVF/intracytoplasmic sperm injection treatment reaching oocyte retrieval, between 1 January 2003 and 31 March 2006. Receiver operator characteristic (ROC) curves were calculated for both parameters, to determine threshold values that might predict OHSS in women with ≥20 oocytes. For the prediction of early onset OHSS, ROC curves showed that an optimal balance between sensitivity and specificity was achieved using thresholds of 24 oocytes (79%, 60%) and 29 follicles (82%, 65%) respectively. Using these thresholds, cryopreservation of all embryos may be offered as an alternative to cancellation of a treatment cycle due to excessive ovarian response, thus minimizing the number of unnecessary interventions while still correctly predicting most cases of early onset OHSS.