A case of a twin surviving to term following the abortion of its co-twin at 9 months in an Arabian mare.
Authors: Derbala M K, Sargious M A N, Hagag N M, Pycock J F, Abu-Seida A M
Journal: Journal of equine veterinary science
Summary
Twin pregnancies in mares typically result in abortion of both fetuses due to placental competition and inadequate space, making this case exceptional: a 7-year-old Egyptian Arabian mare carried one twin to term whilst aborting its co-twin at 9 months of gestation. Notably, the aborted male fetus exhibited severe growth restriction, measuring only 5 months in developmental age whilst its genetically identical co-twin had progressed normally to 9 months; parentage analysis confirmed both fetuses shared the same dam and sire. The survival of one twin despite the loss of the other challenges conventional understanding of twin pregnancy pathophysiology in horses and suggests possible mechanisms including selective placental insufficiency, differential nutritional partitioning between conceptuses, or anatomical factors favouring one twin's development over the other. For practitioners managing twin pregnancies—whether through early detection and selective reduction or expectant management—this report demonstrates that single-twin survival to viability is possible under specific circumstances, though remains rare enough to warrant careful monitoring of heart rates, fetal development symmetry, and placental adequacy throughout gestation. The case also highlights the value of parentage testing in unusual reproductive outcomes to definitively establish genetic relationships and inform prognostic discussions with owners.
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Practical Takeaways
- •Twin pregnancy with selective fetal loss does not inevitably result in abortion of the surviving twin—survival to term is possible though rare
- •Parentage analysis can help confirm genetic relationships and rule out superfetation when unusual twin outcomes occur
- •Close monitoring and supportive management may enable successful completion of gestation even after loss of one twin in mares
Key Findings
- •One twin aborted at 9 months gestation with fetal size equivalent to 5 months of age while co-twin survived to term
- •Both male fetuses were confirmed to be full siblings (same dam and sire) through parentage analysis
- •The surviving twin completed gestation and delivered at term despite the death and abortion of its co-twin
- •This case represents an unusual outcome as twin pregnancy in mares typically results in abortion of both fetuses