pH and the level of calcium in the blood of fetal and neonatal albino rats.

Near-term rat fetuses in utero are acidotic and hypoxic, and have high levels of total serum calcium. In the first hour of postnatal life, pO2 and pH increase and pCO2 and calcium fall. Between 1 and 4 h following birth, respiratory gases vary little, whereas pH continues to rise and calcium further declines. By 4 h, newborns reach normal pH levels but are markedly hypocalcemic. It is suggested that the 'hypercalcemia' of intrauterine life is related to acidosis in utero, and that following birth, the initial fall in serum calcium is associated with the blowing off of CO2 and a concomitant rise in pH. The later decline in circulating calcium is independent of alterations in respiratory gases and relates directly to the final correction of neonatal acidosis.