Intrapartum computerized fetal heart rate parameters and metabolic acidosis at birth.

OBJECTIVE To estimate to what extent computerized fetal heart rate (FHR) parameters are affected by labor and to estimate the relationship between FHR parameters and the degree of fetal metabolic acidosis in laboring patients at term. METHODS Fifty-one women between 37 and 42 weeks' gestational age were recruited prospectively in the following groups: 1) nonlaboring women, and 2) laboring women requiring fetal scalp electrode for continuous electronic FHR monitoring. Computerized FHR analysis was performed for 1 hour within 6 hours of delivery in the nonlaboring group and continuously throughout labor in the laboring group. Multiple linear regression analysis was used to determine the relationship between individual FHR parameters during the last hour before delivery and the degree of metabolic acidosis at birth. RESULTS The umbilical cord artery base excess and pH did not show any significant correlation with any of the computer-derived FHR parameters studied. Both umbilical cord venous base excess and pH were inversely related to the number of large FHR decelerations (r = -.46, P <.01 and r = -.56, P <.01, respectively). Labor was associated with a 31% increase in both short- and long-term FHR variation in the reassuring FHR tracing group when compared with nonlaboring women. Although this increase in FHR variation was not seen in the nonreassuring FHR tracing group, there was no relationship to the degree of metabolic acidosis at birth. CONCLUSION In term pregnant women with reassuring FHR tracing, labor causes an increase in both short- and long-term FHR variation, which was abolished in the presence of nonreassuring FHR tracing. Computer-derived FHR parameters studied during the last hour of labor were not correlated with the degree of metabolic acidosis as measured in the umbilical artery at birth.