Factors affecting angiotensin II concentrations in the human infant at birth.

1. A radioimmunoassay for the measurement of angiotensin II in 1 ml of plasma has been developed and used to measure angiotensin II in maternal peripheral, cord venous and cord arterial blood in 45 patients at delivery. 2. In babies delivered vaginally, cord venous and cord arterial concentrations of angiotensin II were significantly higher than maternal venous blood concentrations. There was a significant relationship between both cord venous and cord arterial concentrations and maternal concentrations of angiotensin II. 3. Cord venous concentrations of angiotensin II were significantly greater than those in cord arterial blood in babies delivered vaginally but not in those delivered by lower-segment Caesarean section. This suggests the possibility that, during labour, the placenta may contribute to foetal concentrations of angiotensin II. 4. Maternal and cord venous concentrations of angiotensin II were significantly higher in patients with hypertensive disease of pregnancy than in those who had remained normotensive throughout pregnancy. 5. Cord venous concentrations of angiotensin II increased significantly with increasing duration of the second stage of labour.