Plasma Renin Levels in the Normal and Anephric Fetus at Birth

(1) Plasma renin activity (PRA), plasma renin concentration (PRC), and renin substrate (RS), have been measured in venous blood samples of 4 healthy women during the second stage of labour and the cord bloods of the 4 infants at delivery. (2) PRA and PRC show a similar range of values in both mothers and fetuses, but fetal renin substrate levels are approximately half the values seen in the maternal samples. (3) There was no plasma renin activity in the cord blood of the anephric fetus, suggesting that biologically active renin does not cross the placenta. Plasma renin concentration was approximately 10% of the level seen in normal infants.