Vasopressin concentration in cord blood: correlation with method of delivery and cord pH.

Cord plasma vasopressin concentration, determined by radioimmunoassay, was higher in arterial than in venous blood in 122 (84%) infants; the highest vasopressin values were recorded in 21 acidotic infants (mean cord pH, 7.13) delivered per vaginam and the lowest values in 50 infants delivered by cesarean section. Cord vasopressin levels were not elevated in infants delivered by cesarean section because of obstructed labor. There was a lack of correlation between vasopressin levels and the length of labor or cervical dilatation; a significant correlation was found between cord arterial vasopressin values and pH. Low vasopressin values were recorded in a group of 22 healthy infants (mean cord pH, 7.29) delivered by low forceps operation.