Formation of the first plane of division relative to the pronuclear axis predicts embryonic ploidy

Abstract

Research QuestionThis study aimed to examine the relationship between the position of male and female pronuclei immediately before the loss of the pronucleus (pronuclear axis) and the formation of the first-division plane in human pronuclear-stage embryos, and its effects on ploidy and clinical pregnancy rates. DesignTransferred embryos were followed up until their prognoses. A total of 762 embryos formed two cells and reached the blastocyst stage after normal fertilisation in a time-lapse incubator. Embryos were classified into three groups: group A, comprising embryos in which the first plane of division was formed parallel to the axis of the pronucleus; group B, comprising embryos in which cases of oblique formation were observed; and group C, embryos in which cases of perpendicular formation were observed. ResultsThe euploidy rate was significantly higher in groups A and B than those in group C (P < 0.01), whereas the aneuploidy rate was significantly higher in group C (P < 0.01) than in groups A and B. There were no differences between the three groups in terms of the frequency of positive human chorionic gonadotropin-based pregnancy tests, frequency of clinical pregnancies, miscarriage rates, or delivery rates. Conclusions: The formation pattern of the first plane of division relative to the pronuclear axis was a predictor of embryonic ploidy, with a reduced rate of euploidy and a high probability of aneuploidy observed when the first plane of division was perpendicular to the pronuclear axis.