O-100 Incidence, morphology, ploidy and developmental arrest in direct cleavage embryos: what are they teaching us? Morphokinetic analysis of 15.081 embryos
Authors: Erberelli R , Nicolielo Barreto M , Jacobs C.K , Motta E.L.A , Alegretti J.R , Lorenzon A.R 
Published: June 2022

Abstract

Study question
What is the impact of direct cleavage (DC) occurrence during embryo/blastocyst development regarding morphology grade, embryo arrest and ploidy status?

Summary answer
Blastocyst formation and morphology grade are significantly reduced in DC when compared to non-DC embryos; however, there is no difference in blastocyst ploidy status.

What is known already
Chromosome instability leading to aneuploidy during early cleavage is well known in humans. DC is defined as the abrupt cleavage of one into three or more daughter blastomeres as the result from an irregular mitosis. Three or more mitosis poles can impair early embryo development; however, how some embryos with these irregular divisions might be able to develop into expanded blastocysts is still unknown. Time-lapse system provides an uninterrupted evaluation of embryo morphological and dynamic parameters, allowing our understanding in such events and if those embryos may be associated with a self-correction mechanism to reach blastocyst stage.

Study design, size, duration
Retrospective cohort study from 15.081 embryos, 3.962 cycles and 3.106 patients that were undergoing in vitro fertilization (IVF) treatment according to medical referral in a single private ART center from December 2018 to November 2021. Only two-pronuclear (2PN) embryos cultured in time-lapse incubators (EmbryoScope, Vitrolife, Sweden) were included in the study. Direct cleavage occurance was annotated when a single blastomere directly cleaved into three or more daughter blastomeres.

Participants/materials, setting, methods
DC embryos were also classified in DC 1-3: abnormal cleavage occurred in zygote (1-cell) resulting in 3–4 blastomeres and in DC 2+: abnormal cleavage occurred at the 2-cell stage resulting in 5 or 6 blastomeres. Embryo arrest, blastocyst formation rate and morphology grade (Gardner and Schoolcraft, 1999) were annotated. Blastocyst biopsy reports for ploidy status were also considered for analysis. Mann-Whitney, chi-squared and Fisher tests were applied for statistical analysis. p &lt; 0,05 was considered significant.

Main results and the role of chance
There were 1168 DC embryos (7,7%) from 896 cycles/841 patients; 502 DC1-3 (3,3%) from 391 cycles/366 patients and 666 DC2+ embryos (4,4%) from 475 patients/505 cycles. In DC group, around 21% of patients have the incidence of more than 1 DC embryo per cycle. Maternal age was lower in DC groups: 38,0±3,61 (DC1-3) and 38,60±3,21 (DC2+) years old versus not-DC (39,02±3,01, p &lt; 0,0001). Embryo arrest was higher (DC1-3:85,5% and DC2+:56,8% versus not-DC:35,4%, p &lt; 0,0001) and blastocyst formation rate was lower (14,5% and 43,2% versus 64,6%, p &lt; 0,0001) in both DC groups and also between DC groups (p &lt; 0,0001). There were 4124 biopsied not-DC blastocysts, 24 in DC1-3 and 154 in DC2+. There was no difference in ploidy between not-DC (57,9%, 40,2%, 1,9%, aneuploid, euploid and mosaic respectively) and DC groups (54,2%, 41,7%, 4,2% and 61%, 37% and 1,9% respectively, p = 0.86) and neither between DC-groups (p = 0.69). Inner cell mass morphology grades were distinct in all groups (not-DC A:45,8%, B:45,2% C:9,0%, DC1-3 A:35,6%, B:33,9%, C:30,5% and DC2+ A:23,1%, B:57,0% C:19,9%, p &lt; 0,0001) and between DC-groups (p &lt; 0,0001). Trophoectoderm morphology grades were also higher for not-DC group (not-DC A:30,5%, B:48,9% C:20,6%, DC1-3 A:15,3%, B:47,5%, C:37,3% and DC2+ A:13,6%, B:44,4% C:42,0%, p &lt; 0,0001), however there was no difference between DC-groups (p = 0.80).

Limitations, reasons for caution
Limited data are available on the implantation potential of embryos with DC, as they are not prioritize for transfer, although our study did not demonstrated a higher aneyploidy rate. Patient parameters, with the exception of maternal age, were not considered in this study.

Wider implications of the findings
Although the morphology grades are lower and embryo arrest is higher in DC embryos, probably due to unequal cleavage, if they reach blastocyst stage, the ploidy status of these embryos are similar to not-DC embryos, speculative for a self-correction mechanism. Future steps should focus on their performance in pregnancy/live-birth.

Trial registration number
Not Applicable