Morphological and morphokinetic associations with aneuploidy: a systematic review and meta-analysis

Abstract

BACKGROUND A time lapse system (TLS) is utilized in some fertility clinics with the aim of predicting embryo viability and chance of live birth during IVF. It has been hypothesized that aneuploid embryos display altered morphokinetics as a consequence of their abnormal chromosome complement. Since aneuploidy is one of the fundamental reasons for IVF failure and miscarriage, attention has focused on utilizing morphokinetics to develop models to non-invasively risk stratify embryos for ploidy status. This could avoid or reduce the costs associated with pre-implantation genetic testing for aneuploidy (PGT-A). Furthermore, TLS have provided an understanding of the true prevalence of other dysmorphisms. Hypothetically, the incorporation of morphological features into a model could act synergistically, improving a model’s discriminative ability to predict ploidy status. OBJECTIVE AND RATIONALE The aim of this systematic review and meta-analysis was to investigate associations between ploidy status and morphokinetic or morphological features commonly denoted on a TLS. This will determine the feasibility of a prediction model for euploidy and summarize the most useful prognostic markers to be included in model development. SEARCH METHODS Five separate searches were conducted in Medline, Embase, PubMed and Cinahl from inception to 1 July 2021. Search terms and word variants included, among others, PGT-A, ploidy, morphokinetics and time lapse, and the latter were successively substituted for the following morphological parameters: fragmentation, multinucleation, abnormal cleavage and contraction. Studies were limited to human studies. OUTCOMES Overall, 58 studies were included incorporating over 40 000 embryos. All except one study had a moderate risk of bias in at least one domain when assessed by the quality in prognostic studies tool. Ten morphokinetic variables were significantly delayed in aneuploid embryos. When excluding studies using less reliable genetic technologies, the most notable variables were: time to eight cells (t8, 1.13 h, 95% CI: 0.21–2.05; three studies; n = 742; I2 = 0%), t9 (2.27 h, 95% CI: 0.5–4.03; two studies; n = 671; I2 = 33%), time to formation of a full blastocyst (tB, 1.99 h, 95% CI 0.15-3.81; four studies; n = 1640; I2 = 76%) and time to expanded blastocyst (tEB, 2.35 h, 95% CI: 0.06–4.63; four studies; n = 1640; I2 = 83%). There is potentially some prognostic potential in the degree of fragmentation, multinucleation persisting to the four-cell stage and frequency of embryo contractions. Reverse cleavage was associated with euploidy in this meta-analysis; however, this article argues that these are likely spurious results requiring further investigation. There was no association with direct unequal cleavage in an embryo that progressed to a blastocyst, or with multinucleation assessed on Day 2 or at the two-cell stage. However, owing to heterogeneous results and poor-quality evidence, associations between these morphological components needs to be investigated further before conclusions can be reliably drawn. WIDER IMPLICATIONS This first systematic review and meta-analysis of morphological and morphokinetic associations with ploidy status demonstrates the most useful morphokinetic variables, namely t8, t9 and tEB to be included in future model development. There is considerable variability within aneuploid and euploid embryos making definitively classifying them impossible; however, it is feasible that embryos could be prioritized for biopsy. Furthermore, these results support the mechanism by which algorithms for live birth may have predictive ability, suggesting aneuploidy causes delayed cytokinesis. We highlight significant heterogeneity in our results secondary to local conditions and diverse patient populations, therefore calling for future models to be robustly developed and tested in-house. If successful, such a model would constitute a meaningful breakthrough when accessing PGT-A is unsuitable for couples.

Time-lapse monitoring technologies for the selection of bovine <i>in vitro</i> fertilized embryos with high implantation potential

“… ) [ 21 ]. Although the mechanisms underlying abnormal cleavage are not fully understood, it has been hypothesized that the causes include sperm quality or DNA damage, chromosomal abnormalities, multipolar spindles, and aberrant centrosomes [ 19 , 22 , 24 , 71 ]. The prevalence of RC has been reported to be 0.4%–27.4% [ 22 , 69 , 72 , 73 ] in humans and 7.6–17.2% in cattle [ 53 , 57 ].…”

“…Both quantitative and qualitative evaluations of embryos during the early developmental stage may be applicable to detect aneuploidy. A recent systematic review in humans reported that the times to 8-cells, 9-cells, blastulation, and expanded blastocyst were prolonged in aneuploid embryos, indicating that these morphokinetic variables have prognostic potential [ 24 ]. Similarly, a bovine IVF study revealed that slowly cleaving embryos had an increased proportion of chromosomal abnormalities compared with rapidly cleaving embryos [ 11 ].…”

“…Fragmentation, abnormal cleavage, contraction, and multinucleation have been postulated as qualitative parameters for screening embryo ploidy status. A human meta-analysis showed that RC is associated with euploidy, whereas DC is not associated with chromosomal abnormality [ 24 ]. However, the authors cautioned that further validation is needed because RC is frequently associated with compromised embryo quality and inferior implantation rates [ 24 ].…”

“…Several human and bovine studies have suggested that a detailed analysis of the timing and pattern of the first post-fertilization cleavage may allow the selection of embryos with a high implantation potential [ 11 , 18 , 19 , 20 , 21 , 22 ]. Furthermore, it has been postulated that TLM can predict the ploidy status of embryos because aneuploid embryos can present morphokinetic differences compared to normal embryos during their development due to aberrant chromosome complement [ 23 , 24 ]. Since aneuploidy is one of the critical causes of implantation failure and miscarriage [ 25 , 26 , 27 ], non-invasive determination of ploidy status using TLM would be beneficial.…”

Automated Grading Of Early Stages Of The Human Embryo Development

“…The embryo goes through perforation at this time, the blastocoel is large enough to push the trophectoderm up against the zona pellucida, and the latter begins to thin. This is when the to cleavage is defined as the first observed frame in which the newly formed blastomeres are completely separated by epithelial cell membranes (11)(12)(13)(14)(15)(16)(17)(18)(19)(20).…”