Endogenous plasma epinephrine and norepinephrine in last-trimester pregnancy and labor.

Plasma epinephrine and norepinephrine concentrations during labor and immediately after delivery were compared to those of the third trimester in 21 uncomplicated pregnancies of married primigravid women, 20 to 32 years old. Third-trimester catecholamine concentrations were similar to those of normal, nonpregnant subjects; samples were obtained under identical conditions. Compared to third-trimester levels, significant elevations of plasma epinephrine and norepinephrine were found in three phases of labor (at 3 to 5 cm. and 9 to 10 cm. of cervical dilatation and immediately after delivery). Epinephrine values returned to normal within three to 21 minutes after delivery; norepinephrine values remained high or continued to rise in this time interval. Maternal analgesia and anesthesia influenced plasma catecholamine levels.