Daily changes in foetal and maternal blood of conscious pregnant ewes, with catheters in umbilical and uterine vessels

1. Blood gas tensions, pH, packed cell volume (PCV) and the levels of glucose, fructose and lactic acid have been followed in foetal and maternal blood for periods of 3-30 days in conscious ewes between 80 days gestation and term ( approximately 147 days).2. Blood samples were withdrawn through indwelling catheters placed in one or both umbilical vessels, a uterine vein and a maternal artery.3. The success of the operation appeared to depend on the maintenance of maternal blood gas and pH levels within normal limits as well as on the final position of the tip of the catheter. The difficulties and limitations of the technique are discussed.4. Foetal blood gas tensions, pH, PCV, lactic acid and glucose levels did not change markedly during the last 50-60 days of gestation. The fructose concentration fell during this period, the greatest change was between 100 and 120 days gestation.5. Small fluctuations in P(O2), P(CO2) and pH in umbilical venous blood were associated with similar changes in the uterine vein, so that the gradients across the placenta appeared to remain constant.6. Daily changes in maternal plasma glucose levels were reflected in similar changes in foetal plasma fructose and by much smaller alterations in the foetal glucose levels. The glucose concentration in the foetal plasma was less than 25% of that in maternal plasma.7. The existence of a general relationship between maternal plasma glucose and foetal plasma fructose was masked by the independent fall in fructose levels with age. However, at any given stage of gestation, there was a significant correlation between foetal fructose and maternal glucose.8. Few changes in the umbilical blood were associated with impending abortion or birth. Blood gas tensions remained constant, but a sharp fall in fructose levels often occurred 48 hr before any changes in pH, PCV and lactate concentration.9. Present and other findings on conscious animals are compared with previous observations on acute, anaesthetized preparations.