Partition of maternal nutrients to the placenta and fetus in the sheep

Utilizing the Fick Principle, the fluxes of oxygen and glucose leaving the uterine circulation and entering the fetal umbilical circulation were measured simultaneously in 35 chronically catheterized sheep. Additionally, the distribution of placentally produced lactate into the uterine and umbilical circulations was measured by the same techniques. Under unstressed conditions, placental oxygen consumption accounted for approximately half the oxygen exiting the uterine circulation. Placental glucose consumption averaged 75% of the glucose exiting the uterine circulation, and this proportion increased with decreasing glucose concentration in the maternal artery. Lactate was produced at a high rate by all placentae, and distributed disproportionately to the fetus, in spite of higher fetal lactate concentration. Fetal metabolism was aerobic, as demonstrated by a high rate of net oxygen consumption and a high rate of net lactate consumption. Fetal oxygen metabolism correlated well with fetal weight and with the sum of net fetal lactate and glucose consumption.