Value of transferring embryos derived from monopronucleated (1PN) zygotes at the time of fertilization assessment

Summary This paper is a retrospective analysis of the sole transfer of monopronucleated zygotes (1PN) embryos both in in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) to determine the value of transferring embryos formed from 1PN. In fresh cycles, 1PN cleavage-stage embryos (1PN cleavage fresh) were transferred. In frozen–thawed cycles, 1PN blastocyst-stage embryos (1PN blast frozen) were transferred. We used comparison groups: for fresh cycles, 2PN cleavage-stage embryos (2PN cleavage fresh) were transferred; and for frozen–thawed cycles, 2PN blastocyst-stage embryos (2PN blast frozen) were transferred. Comparison groups were matched for cycle and patient characteristics to the 1PN group. Finally, for fresh cycles, live birth rates (LBR) in the 1PN cleavage group were significantly lower than those in 2PN cleavage group, both for IVF [LBR = 7.64% vs. pregnancy rate (PR) = 22.12%, P = 0.003, respectively] and ICSI (LBR = 0% vs. LBR = 20.00%, P < 0.001, respectively). For frozen–thawed IVF cycles, the PR in the 1PN blastocyst group were comparable with those of the 2PN blastocyst group (1PN: LBR = 33.14% vs. 2PN: LBR = 37.24%, P = 0.289, respectively), while in ICSI, the PR in the 1PN blastocyst group were lower than those in the 2PN blastocyst group (LBR = 15.25% vs. LBR = 40.68%, P = 0.002, respectively). So, for IVF, blastocyst culture was capable of selecting normal 1PN embryos for transfer and achieves satisfying outcomes. However, for ICSI, blastocyst culture was not effective enough to eliminate abnormal embryos and 1PN embryo transfer needed to be treated with caution.