Ultrasound-guided fetal thorax compression to reduce post-fixation twins in the mare.
Authors: Arnold Leonie C, Stout Tom A E, Claes Anthony N J
Journal: Equine veterinary journal
Summary
# Editorial Summary: Ultrasound-guided Twin Reduction in Mares Twin pregnancies in horses present a significant clinical challenge, particularly after the conceptuses have become fixed to the uterine wall around 50 days of gestation, as conventional reduction methods are either invasive, technically demanding or unreliable. Arnold and colleagues evaluated transrectal ultrasound-guided fetal thorax compression in 16 mares presenting with fixed twins between 51–79 days of gestation, performed by two experienced operators who selectively compressed one fetus under real-time ultrasound imaging. The technique achieved an overall success rate of 56% (9 of 16), but with striking variation depending on twin type: 90% success with dizygotic twins (9 of 10) versus complete failure with monozygotic twins (0 of 6), likely reflecting the physiological complications of shared placentation and single chorion in identical twins. Among the successfully reduced dizygotic pregnancies, seven mares subsequently delivered healthy, normally-sized foals, though two losses occurred between clinic discharge and parturition. For practitioners managing fixed dizygotic twins, this minimally-invasive ultrasound-guided approach offers a realistic alternative to more aggressive surgical techniques, though twin genotype must be established beforehand—ideally via earlier embryonic assessment—as monozygotic cases appear unsuitable for this intervention and may warrant different management strategies.
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Practical Takeaways
- •Transrectal ultrasound-guided thorax compression offers a minimally-invasive option for twin reduction in mares carrying dizygotic twins, with approximately 70% chance of delivering a live foal
- •This technique should not be attempted for monozygotic twin pregnancies as it has zero success rate for live birth outcomes
- •Procedure timing around 2 months gestation and twin zygosity determination via ultrasound are critical factors for case selection and client counselling regarding realistic success expectations
Key Findings
- •Transrectal ultrasound-guided fetal thorax compression successfully reduced 9 of 16 (56%) twin pregnancies overall
- •Success rate was significantly higher in dizygotic twins (9/10, 90%) compared to monozygotic twins (0/6, 0%)
- •Among successful dizygotic reductions, 7 of 9 mares delivered healthy foals of normal size, with 2 mares losing pregnancy after discharge
- •Procedure was performed between 51-79 days of gestation as a minimally-invasive alternative to more invasive reduction techniques