Intramuscular pethidine (meperidine) during labor associated with metabolic acidosis in the newborn.

Analyses of fetal heart rate (FHR) variability, visual evaluation of FHR decelerations, and respiratory gas analyses of the umbilical vein were performed in 27 labors, where one dose (50 or 75 mg) of intramuscular pethidine was used for pain relief, in 47 labors with one paracervical blockade (6 ml 0.5% marcaine) and in a control group of 135 labors without any pain relief. Umbilical vein pH, standard bicarbonate and base excess were lowest in the pethidine group and highest in the PCB group. The duration of labor was shortest in the control group, but there was no difference in the duration of labor of the two anesthesized groups. Intramuscular pethidine seems to associate with umbilical metabolic acidosis and PCB should be preferred to it, when an obstetrician is available.