Are tri-pronuclear embryos that show two normal-sized pronuclei and additional smaller pronuclei useful for embryo transfer?

Purpose: This study aimed to analyze whether tripronuclear (3PN) zygotes, with two normal-sized PNs and an additional smaller PN (2.1PN), can be used for embryo transfer.

Methods: A retrospective embryo cohort study was conducted on 695 patients who underwent intracytoplasmic sperm injection treatment. Blastocyst formation rates were compared between 2.1PN and 2PN zygotes and PGT-A analysis was performed on 15 blastocysts derived from 2.1PN zygotes.

Results: Blastocyst formation rates were comparable between 2.1PN (43.8%) and 2PN zygotes (54.8%; p = 0.212). The rates of blastocysts with good morphology derived from 2.1 PN and 2PN zygotes were 18.8% and 25.5%, respectively. No significant differences were detected (p = 0.383). All of the analyzed blastocysts were diploid; however, 13 of these were found to be aneuploid, with a further two being mosaic.

Conclusion: Our results suggest that 2.1PN embryos can reach blastocyst stage. These blastocysts were diploid, however, predominantly aneuploid, and therefore could not be used for embryo transfer.