Clinical pregnancy outcomes after transfer of fresh and vitrified-warmed conventional IVF equine embryos.

Overview

• This study investigated pregnancy outcomes in horses using embryos produced by conventional in vitro fertilization (cIVF), comparing fresh embryos versus those that were vitrified (cryopreserved) and then warmed before transfer.
• The research assessed early pregnancy rates and embryonic heartbeat detection to evaluate the success of embryo transfer using both fresh and vitrified-warmed embryos.

Background

• Assisted reproductive technologies (ART) like IVF have become important tools in equine breeding.
• Conventional IVF involves fertilizing horse eggs with sperm in a laboratory setting to produce embryos outside the mare’s body.
• Cryopreservation (freezing) of embryos can facilitate flexible timing for embryo transfer and improve management of breeding programs.
• Vitrification is a rapid freezing technique that prevents ice crystal formation and is commonly used for embryo preservation.
• However, the impact of vitrification on embryo viability and subsequent pregnancy outcomes in horses is not well established.

Study Objectives

• To report clinical pregnancy outcomes following transfer of cIVF equine embryos that were either fresh or vitrified and warmed.
• To compare early pregnancy rates and embryonic viability indicators between these two embryo groups.

Methods

• A total of 40 equine embryos were produced by conventional IVF.
• Embryos were either:
  • Transferred fresh into recipient mares, or
  • Vitrified (cryopreserved) then warmed before transfer.
• Pregnancy diagnosis was conducted 6 days after embryo transfer to determine initial pregnancy establishment.
• Embryonic heartbeat—a sign of continued development and viability—was checked between days 25 and 30 of gestation.
• Pregnancy rates and heartbeat detection percentages were recorded along with 95% confidence intervals.

Results

• Fresh embryo group:
  • Pregnancy rate at 6 days post-transfer: 81% (17 out of 21 recipients; 95% CI: 58% to 95%).
  • Embryonic heartbeat detected in 94% of established pregnancies (16/17; 95% CI: 71% to 100%).
• Vitrified-warmed embryo group:
  • Pregnancy rate at 6 days post-transfer: 79% (15 out of 19 recipients; 95% CI: 54% to 94%).
  • Embryonic heartbeat detected in 100% of established pregnancies (15/15; 95% CI: 78% to 100%).

Interpretation and Limitations

• Pregnancy rates for both fresh and vitrified-warmed embryos were similar, suggesting vitrification may not compromise early pregnancy establishment.
• The high proportion of embryonic heartbeats indicates good embryo viability following both protocols.
• Results are descriptive due to:
  • Retrospective study design (reviewing past cases rather than planned prospective trial).
  • Relatively small sample size (40 embryos total).
  • Potential variability in recipient mare management and embryo characteristics.
• Because of these limitations, definitive conclusions about comparative efficacy cannot be drawn from this data alone.

Conclusions and Future Directions

• This study contributes important clinical data on pregnancy outcomes after transfer of cIVF equine embryos.
• Findings support the idea that vitrification of conventional IVF embryos is feasible without obvious reduction in early pregnancy success.
• Emphasizes need for larger, well-controlled prospective studies to:
  • Better evaluate the effectiveness of vitrification in equine IVF embryos.
  • Control for recipient mare management and embryo quality variables.
  • Improve evidence-based recommendations for clinical use of cryopreserved embryos in horses.