Birth of a Healthy Monozygotic Twin Foal with Hydrops and a Dead Co-Twin

Transfer of in vitro-produced (IVP) equine embryos is associated with a higher incidence of monozygotic multiple pregnancies, but this remains a rarity. The outcome of monozygotic twin gestation is poor, and good management techniques are lacking. In addition, hydrops conditions are exceptional in horses, with hydroallantois occurring more frequently than hydramnion. Most hydrops conditions will lead to compromise or death of the foal and mare. A 6-year-old multiparous standardbred recipient mare, 332 days pregnant, diagnosed with a monozygotic twin and hydrops with a dead co-twin, gave birth with an assisted vaginal delivery. The dead foal, previously determined at 9 months by ultrasound, turned out to have the dimensions and hair corresponding to an 8-month-old foal. The other foal was born alive and considered healthy and normal-sized for its age. Both mare and foal were discharged from the clinic one week after parturition. This report is the first to describe the birth of a healthy foal born from a monozygotic twin pregnancy in the presence of hydrops, following transfer of a single IVP equine embryo. In addition, it is rare to find a non-macerated, non-mummified dead co-twin after fetal death at 8 months together with a healthy full-term foal.