Arginine vasopressin during gestation and parturition in sheep fetus

The possible correlation between plasma arginine vasopressin (AVP) concentration and the processes leading to parturition was assessed in 11 chronically catheterized pregnant ewes. Samples of blood withdrawn intermittently during a 20-day period preceding labor and during parturition were analyzed for AVP by a specific radioimmunoassay, as well as for pH, PaCO2 and PaO2. Fetal AVP was 1.74 +/- 1.55 pg/ml and maternal AVP 1.47 +/- 0.74 pg/ml (mean +/- SD). No preparturient rise in fetal vasopressin was noted, but levels increased progressively during labor to reach peak levels in cord blood (range 7.5--8,000 pg/ml). There was no consistent rise in maternal vasopressin during the same interval. A relationship between prolonged antepartum intrauterine asphyxia and increases in fetal vasopressin was noted. It is concluded that the markedly elevated levels of vasopressin observed in cord blood are the result of intrapartum 'stress', but are not related to the initiation of parturition.