Effects of Single Umbilical Artery Ligation in the Lamb Fetus

The effects of single umbilical artery ligation have been studied in 20 lamb fetuses, using chronic indwelling catheters placed in a retrograde fashion via the ligated umbilical artery in the fetal aorta. Fetal arterial blood pressure, heart rate, blood pH, PCO2 and PO2 were monitored at various intervals until the end of the gestation. The results indicate that prolonged fetal survival is possible. Although fetuses near term did not survive this insult, long-term survival (3 to 56 days) was observed in nine animals of earlier gestational age. After an initial period of hypoxia, acidosis, and hypercapnia, stabilization occurred and "normal" values for these parameters were observed. In spite of the apparently normal gas and hydrogen exchange between mother and fetus, profound fetal malnutrition was observed in two animals who survived 26 and 56 days, respectively. The possible mechanisms of fetal adaptation to this acute change in intra-uterine environment and the potential value of this "experimental model" for studying chronic fetal distress due to placental insufficiency are discussed.