Spatiotemporal perturbations of pronuclear breakdown preceding syngamy affect early human embryo development: a retrospective observational study.

Purpose: During fertilisation, female and male pronuclei (PNs) migrate to the centre of the ooplasm, juxtapose, and break down synchronously in preparation for the first mitosis. While PN non-juxtaposition and PN breakdown (PNBD) asynchrony are occasionally observed, their developmental implications remain uncertain. This study investigated the possible relationships among the two phenomena, preimplantation development patterns, and live birth rates in single blastocyst transfers.