Value of transferring embryos that show no evidence of fertilization at the time of fertilization assessment

Objective To determine the value of transferring embryos formed from nonpronuclear (0PN) zygotes. Design A case-control study. Setting Not applicable. Patient(s) The current study was a retrospective analysis of embryo transfers of just 0PN embryos using fresh cleavage-stage embryos (0PN cleavage fresh), frozen-thawed cleavage-stage 0PN embryos (0PN cleavage frozen), and frozen 0PN blastocyst-stage embryos (0PN blast frozen). Intervention(s) To study the effect of 0PN transfer, comparison groups were used: fresh cycles of 2PN (2PN cleavage fresh-C) and frozen-thawed cycles cleavage-stage (2PN cleavage frozen-C) and blastocyst-stage (2PN blast frozen-C). Comparison groups were matched for cycle and patient characteristics to the 0PN group. Main Outcome Measure(s) Implantation rate (IR), pregnancy rate, and transferable embryo rate. Result(s) For fresh cycles, the IR in the 0PN cleavage fresh was lower than that in the 2PN cleavage fresh-C (8.04% vs. 19.50%, respectively). For frozen-thawed cycles, the IR in the 0PN cleavage frozen was lower than that in the 2PN cleavage frozen-C (15.38% vs. 28.24%, respectively), but the IR in 0PN blast frozen was comparable to that of 2PN blast frozen-C (39.56% vs. 48.18%, respectively). Conclusion(s) Transfer of 0PN embryos from fresh or frozen-thawed cycles results in pregnancies and live births. Nonpronuclear embryos have a lower IR than 2PN embryos, but if the embryos are cultured to the blastocyst stage and then are frozen, their IRs approach that of 2PN embryos in subsequent frozen-thawed cycles. The culture of 0PN embryos to the blastocyst stage may select for embryos with a near-normal IR.