Abnormal cleavage may help flag equine embryo loss risk
Bottom line
Abnormal cleavage patterns in equine IVP embryos may signal pregnancy loss risk. A new retrospective study in Equine Veterinary Journal found that equine in vitro-produced embryos showing abnormal first-cleavage patterns were less likely to establish pregnancy and more likely to be lost early after transfer than embryos with normal cleavage. Among transferred embryos, total early pregnancy loss reached 53.3% in embryos with abnormal cleavage patterns, versus 22.6% in those with normal patterns. The study also found that embryos reaching vitrification sooner, a proxy for faster blastocyst development, had better odds of pregnancy at 14 days and lower loss through 25 days. The work was led by Soledad Martin-Pelaez and colleagues, and adds a new morphokinetic signal to embryo selection in equine assisted reproduction. (citedrive.com)
Why it matters: For veterinarians and reproduction teams, the findings suggest that time-lapse assessment of the first mitotic division could help refine which IVP embryos are most suitable for transfer, especially as the field continues to grapple with higher loss rates in IVP embryos than in vivo-derived embryos. Prior work has shown that pregnancy and foaling outcomes in equine IVP are tied to developmental speed and embryo quality, but standardized classification criteria remain limited. Adding cleavage-pattern data could improve counseling for pet parents and breeding clients, help prioritize embryos for transfer or cryopreservation, and potentially narrow the outcome gap between IVP and conventional embryo production. (citedrive.com)
What to watch: Whether clinics begin validating time-lapse cleavage scoring prospectively, and whether embryo grading systems are updated to incorporate these early morphokinetic markers. (citedrive.com)
Key facts
- Study type
- Retrospective study
- Journal
- Equine Veterinary Journal
- Species
- Equine
- Sample size
- 70 transferred IVP embryos with known pregnancy outcomes, plus 114 arrested embryos
- Main finding
- Abnormal first-cleavage patterns were linked to lower pregnancy rates and higher early pregnancy loss
- Early pregnancy loss
- 53.3% with abnormal cleavage, 22.6% with normal cleavage
- Additional finding
- Earlier vitrification, a proxy for faster blastocyst development, was associated with better pregnancy odds at 14 days and lower loss through 25 days
- Lead author
- Soledad Martin-Pelaez
A new study in Equine Veterinary Journal suggests that what happens during an equine embryo’s very first cell division may carry meaningful clinical value. Researchers reported that abnormal cleavage patterns in in vitro-produced, transferred equine embryos were associated with both lower pregnancy rates and substantially higher early pregnancy loss, with total early loss of 53.3% in abnormal-cleavage embryos compared with 22.6% in normal-cleavage embryos. Faster progression to vitrification, reflecting earlier blastocyst formation, was also linked to better early outcomes. (citedrive.com)
That matters because equine in vitro embryo production has advanced steadily, but embryo selection remains less standardized than many clinicians would like. Reviews of the field have noted that IVP embryos, most commonly produced via ICSI, can differ morphologically from in vivo-derived embryos, and pregnancy loss has remained a persistent concern even as technical success has improved. Earlier studies have also linked developmental speed, embryo grade, and morphology with pregnancy and foaling outcomes, reinforcing the idea that embryo competence may be visible before transfer if clinicians know what to look for. (beva.onlinelibrary.wiley.com)
In the new retrospective analysis, the authors reviewed time-lapse images and clinical records from 70 transferred IVP embryos with known pregnancy outcomes, alongside 114 arrested embryos. They examined morphokinetic features of the first mitotic division, compared normal and abnormal cleavage patterns, and modeled associations with pregnancy at 14 days and early pregnancy loss at 25 and 42 days. The key signal was clear: abnormal cleavage reduced the odds of pregnancy and increased the odds of loss, while earlier vitrification improved the odds of pregnancy at day 14 and reduced losses through day 25, though not between days 25 and 42. (citedrive.com)
The findings fit with a broader body of equine reproduction research showing that embryo developmental tempo matters. A 2023 study of 316 equine IVP blastocysts found overall pregnancy and foaling rates of 76.9% and 56.3%, respectively, and identified relationships between developmental characteristics and outcome. Other work has shown that pregnancy loss after transfer of cryopreserved IVP equine embryos remains an important limiting factor, and AAEP proceedings have highlighted roughly 20% pregnancy loss as an ongoing issue for in vitro-produced embryos. (pubmed.ncbi.nlm.nih.gov)
I didn’t find a separate institutional press release or formal expert commentary tied specifically to this paper. Still, the study’s conclusions align with long-running expert discussion in the field: IVP embryo assessment in horses is still evolving, and morphology alone may not capture all the signals that matter. Reviews from leaders in equine embryology have emphasized that quality assessment for IVP embryos is still relatively immature, particularly compared with more established embryo evaluation systems in other species. (pubmed.ncbi.nlm.nih.gov)
Why it matters: For veterinary professionals working in equine theriogenology, this study points to a practical next step in embryo selection: combining conventional morphology with time-lapse morphokinetics, particularly first-cleavage behavior and speed to blastocyst formation. If validated prospectively, that could improve transfer decisions, reduce avoidable early losses, and give veterinarians stronger evidence when setting expectations with pet parents, donor-mare clients, and recipient programs. It may also support more consistent lab-to-clinic communication, since cleavage abnormalities could become a reportable quality parameter rather than an internal observation. (citedrive.com)
There are still important caveats. This was a retrospective study, and the authors note that a larger number of embryo transfers could uncover additional interactions among morphokinetic features. It also doesn’t establish whether abnormal cleavage is a direct cause of pregnancy failure or a marker for deeper developmental issues, such as chromosomal or metabolic abnormalities. That question remains relevant in horses, where the causes of early pregnancy loss are often multifactorial and not fully defined. (citedrive.com)
What to watch: The next step will likely be prospective validation in commercial and academic IVP programs, followed by possible incorporation of cleavage-pattern scoring into simplified grading systems and transfer protocols if the signal holds up across larger datasets. (pubmed.ncbi.nlm.nih.gov)