Abnormal Cleavage Pattern of Preimplantation Human Embryos: Characteristics of Patients and Fertility Treatment Outcomes

Objective:
To assess incidence of abnormal cleavage among humen embryos; compare other morphokinetic parameters of embryos with normal and abnormal cleavage.

Design:
Retrospective analysis of prospectively collected data in a single-center IVF clinic. Analysis of the morphokinetics of embryos with early and late cleavages as identified by time-lapse microscopy. The study included 1001 women who underwent 1976 assisted reproduction treatments during 2016-2021. Irregular cleavage incidence and association with women’s characteristics and pregnancy outcome were evaluated.

Results:
Incidence of irregular cleavage (IRC) was 17.5% (1,684/9,609 embryos). Of these 85% were with early IRC (occurring in less than 50 hours from fertilization) and 15% with late IRC (occurring after more than 50 hours from fertilization). 7,926 embryos were with no IRC, 1,464 embryos were with one IRC, and 219 embryos were with two or more IRC.

Blastocyst formation rate was 19.9%, 20.8%, 11.4% for embryos with no IRC, one IRC, and two or more IRC respectively (p-value 0.004). Blastocyst formation rate was 19.8% in early IRC group, and 18.4% in late IRC group (p-value 0.61).

Either transfer or freeze rate was 53.9%, 14%, and 9.5% for embryos with no IRC, one IRC, and two or more IRC respectively (p-value <0.001). Either transfer or freeze rate was 12.7% in early cleavage group, and 18.4% in late cleavage group (p-value 0.013).

Conclusions:
Amount of abnormal cleavage events and their timing are of great importance for the prognosis of blastocyst formation rate and important factors for optimization of selection criteria for embryo transfer and cryopreservation.