Hydramnios causing uterine rupture in a mare.

An 18-year-old mare, 285 days pregnant, was evaluated for apparent abdominal pain of 8 hours' duration. A large volume of sanguinous fluid was obtained on abdominocentesis, and digital vaginal examination revealed a dilated cervix and blood in the uterus. Abdominal palpation per rectum revealed the uterus to be large and distended with fluid. Ultrasonography revealed a dead fetus on the floor of the cranial portion of the abdomen. The mare was euthanatized, and necropsy confirmed that the uterus had ruptured, and that the fetus, within its chorioallantois, was in the abdomen. The amniotic sac contained approximately 96 L of amniotic fluid. Torsion of the amniotic sac separated the fetus from the fluid-filled compartment. Hydramnios was diagnosed on the basis of the excessive amniotic fluid and was believed to be the cause of the uterine rupture.