Abnormal cleavage may help predict early loss in equine IVP embryos

Abnormal cleavage during the earliest stages of equine in vitro embryo development may be an important warning sign for pregnancy failure after transfer, according to a new study in Equine Veterinary Journal. The retrospective analysis found that embryos showing abnormal cleavage patterns were less likely to establish pregnancy by day 14 and more than twice as likely to be lost before day 42 of gestation than embryos with normal cleavage. The work adds a potentially practical screening signal for clinics using intracytoplasmic sperm injection, or ICSI, to produce transferable equine embryos. (pubmed.ncbi.nlm.nih.gov)

That matters because equine in vitro embryo production has expanded quickly, especially for mares with subfertility, performance schedules, or high genetic value, but the field still lacks the kind of standardized embryo grading systems seen in human IVF. UC Davis’ equine reproduction program describes IVEP as a 9- to 11-day process in which oocytes are collected, matured in the lab, fertilized by ICSI, and cultured to the blastocyst stage, with roughly 30% of fertilized oocytes reaching embryo stage. The same program has highlighted growing interest in non-invasive time-lapse monitoring to identify embryos with the best chance of producing an ongoing pregnancy. (cehhorsereport.vetmed.ucdavis.edu)

In the new study, investigators retrospectively reviewed time-lapse recordings from transferred embryos with known outcomes and from embryos that arrested during culture. Cleavage was classified as normal or abnormal. The overall incidence of abnormal cleavage was about 41%, and abnormal cleavage did not appear to predict whether an embryo would reach the blastocyst stage or the stage at which arrest occurred. But once those embryos were transferred, the differences became clinically meaningful: pregnancy diagnosis at 14 days post-transfer was 62% for abnormally cleaved embryos versus 83% for normally cleaved embryos, and early embryonic loss before 42 days was 53% versus 20%, respectively. The authors’ interpretation is that some embryos can still form blastocysts despite first-division errors, but those defects may be incompatible with continued development after implantation-related demands increase. (2eb88d5a26c9d8f57ffb-aeafbf82c2963100e9056663ea595989.ssl.cf1.rackcdn.com)

The findings also fit with broader work in equine assisted reproduction showing that embryo competence is shaped by more than one factor. Prior clinical studies have found that pregnancy and embryonic loss after transfer of IVP embryos are influenced by donor mare age and identity, embryo development speed, recipient management, and transfer timing. More recent program-level data from Utrecht researchers reported that one or more blastocysts were produced in 78% of procedures and that pregnancy after transfer of thawed IVP blastocysts approached 78% in a 2021 cohort, while emphasizing that donor mare, stallion, recipient mare, and embryonic variables all affect success. In that context, cleavage-pattern assessment may become one more layer of triage rather than a standalone predictor. (research-portal.uu.nl)

Direct outside commentary on this specific paper was limited in open sources, but the broader expert view is consistent: early developmental abnormalities in IVP embryos likely reflect underlying chromosomal instability or mitotic errors that are not always visible on conventional morphology checks. Utrecht University researchers studying large-animal IVF note that equine embryos, like human embryos, appear predisposed to chromosome instability, which can impair implantation and contribute to pregnancy loss. That helps explain why time-lapse systems are attracting attention: they may capture biologically meaningful events that static grading misses. (uu.nl)

Why it matters: For veterinarians and reproduction specialists, the practical takeaway isn’t just that abnormal cleavage is associated with loss, but that it may be detectable early enough to change decision-making. If time-lapse review can identify embryos with lower odds of sustained pregnancy before transfer, clinics may be able to improve embryo prioritization, set more realistic expectations for pet parents, and refine how they allocate recipient mares and laboratory resources. It could also support more standardized reporting in a segment of equine reproduction where embryo quality assessment remains less mature than demand for IVEP services. (pubmed.ncbi.nlm.nih.gov)

There are still important caveats. This was a retrospective study, and the sample of transferred embryos was modest, so the findings should be validated prospectively and across additional programs before they’re treated as universal thresholds. It’s also not yet clear whether abnormal cleavage should trigger non-transfer, altered counseling, genetic testing, or simply lower ranking relative to otherwise similar embryos. The study supports cleavage pattern as a useful classification criterion, but not as the only one. (pubmed.ncbi.nlm.nih.gov)

What to watch: The next step will likely be prospective studies that combine time-lapse morphokinetics with other embryo-quality markers, including developmental speed and, potentially, genetic screening, to see whether clinics can reduce early pregnancy loss without sacrificing transfer volume. If those data hold up, time-lapse monitoring could move from a research-forward feature to a more routine part of equine IVEP workflow. (cehhorsereport.vetmed.ucdavis.edu)