The effect of reverse cleavage on embryo development and clinical outcomes

How does reverse cleavage affect in-vitro embryo development, including the incidence of dysmorphisms such as multinucleation and trichotomous mitosis, and what are the implications for clinical outcomes, such as implantation and live birth rates, when using time-lapse observations?

Clinical retrospective cohort study including 23,814 embryos from 4004 intracytoplasmic sperm injection treatment cycles carried out between November 2014 and October 2019 using fresh oocytes and single blastocyst transfers. Data from patients and cycles were used to address whether they were related to the presence of reverse cleavage. Rates of dysmorphisms, in-vitro development, implantation and live birth successful delivery were compared between embryos with (reverse cleavage positive) and without (reverse cleavage negative) reverse cleavage.

Reverse cleavage was observed at least once in 2.1% of embryos. Compared with reverse cleavage negative embryos, reverse cleavage positive embryos had a significantly (P < 0.001) higher incidence of multinucleation (45.6% versus 19.1%) and trichotomous mitosis (45.4% versus 10.3%). Although only 27.7% of the reverse cleavage positive embryos developed into high-quality blastocysts (significantly lower than reverse cleavage negative embryos; 50.7%, P < 0.001), implantation and live birth rates were similar between the two groups (40.4% [19/47] versus 48.1% [2360/4902] and 31.9% [15/47] versus 32.1% [1571/4902], respectively).

Embryos that overcome reverse cleavage and reach a transferrable stage on day 5 or 6 of culture have the same reproductive potential as embryos without reverse cleavage. Reverse cleavage may involve a mechanism for detecting and repairing errors during embryo development.