Blastocyst-stage versus cleavage-stage embryo transfer in the first frozen cycles of OHSS-risk patients who deferred from fresh embryo transfer.

Elective cryopreservation of all embryos has been the most effective means to avoid developing ovarian hyperstimulation syndrome (OHSS). However, it is still unknown which stage is optimal for freezing and transferring into uterus in OHSS-risk patients. This study was undertaken to evaluate whether OHSS-risk patients could benefit from transferring blastocysts. A total of 162 women were allocated to cleavage-stage embryo transfer (ET) (group A = 70) and blastocysts transfer (group B = 92) on the basis of patients' voluntary in their first frozen cycles. Although the mean number of transferred embryos in group A was significantly more than those in group B (2.37 ± 0.52 versus 2.11 ± 0.52, p < 0.05), the clinical pregnancy rates, implantation rates and live birth rates in group B were significantly higher than those in group A (47.83% versus 31.43%, p < 0.05; 31.44% versus 18.67%, p < 0.05; 40.21% versus 27.14%, p < 0.05), and the multiple pregnancy rates in both groups were comparable (34.09% versus 36.36%, p > 0.05). The observed results in OHSS-risk population allow us to take a position in favor of blastocyst transfer, thus pregnancy and live birth could be achieved with fewer ETs and in a shorter time frame.