Cortisol levels in maternal venous and umbilical cord arterial and venous serum at vaginal delivery.

To provide evidence that the high levels of cortisol found in mixed cord serum at spontaneous delivery are derived from the fetus rather than the mother, arterial and venous cord samples were collected separately along with simultaneous maternal venous samples at term. In the group with spontaneous labor, the difference between umbilical arterial levels of cortisol (78.6 +/- 4.1 ng. per milliliter) exceeded venous levels (61.9 +/- 4.1 ng. per milliliter) (P less than 0.0001). In the group with induced labor, the arterial level (58.4 +/- 6.9 ng. per milliliter) did not differ significantly from the venous level (50.6 +/- 5.9 ng. per milliliter) (P greater than 0.05). In four cases where spontaneous rupture of the membranes occurred prior to induction, values were similar to those of the group with spontaneous labor. The arterial levels of the group with spontaneous labor exceeded those of the group with induced labor (P less than 0.02). These differences cannot be related to duration of labor, gestational age, or maternal cortisol concentration, none of which differed between the group with electively induced and spontaneous labor. The present data provide further evidence that a rise in fetal cortisol production independent of the mother precedes and is involved in the mechanism initiating the spontaneous onset of human labor.