The use of intravascular catheters for long-term studies on the mare and fetus

Methods developed for the insertion of catheters into the umbilical artery and vein and the uterine vein of the pregnancy mare are described. The technique requires careful anaesthesia and the maintenance of normal blood gas tensions, pH and arterial blood pressure. Fetal survival was variable: three mares delivered live foals and six fetuses survived more than 15 days with a maximal period of 41 days. The erythrocytes sedimentation rate (ESR) of the fetal foal was always very low at operation but subsequently increased slightly; a sudden large rise in ESR usually indicated imminent fetal death. The relatively sudden death in utero of catheterized fetuses maintained for 10 days or more remains unexplained. Nevertheless, the stability and relatively long duration of some of these preparations are sufficient to investigate various aspects of placental exchange and the endocrine climate of the fetus.