The efforts toward reducing adverse anesthesia-related maternal and neonatal outcomes are an important aspect of labor analgesia. Present results found no significant difference in the baseline characteristics of parturients (age, prenatal weight, BMI, prenatal WBC, and HGB) and neonates (gestational age, birth weight, and delayed cord ligation time) between the epidural analgesia and non-epidural groups. Apgar scores of the two groups at 1 and 5 minutes after birth also did not show any difference. Our results confirmed that the stages of laboring were significantly longer in the epidural analgesia group compared to the non-epidural group. The lactate value of the umbilical artery blood in the painless delivery group was significantly higher than that in the non-epidural delivery group, and the pCO2 of the umbilical vein blood in the painless delivery group was also significantly increased, suggesting that epidural analgesia usage during labor may have adverse effects on newborns.
Painless delivery technology is the gold standard to reduce pain during labor. Although a large amount of literature reports that painless delivery is beneficial, the impact on maternal and neonatal outcomes is still controversial. In this study, the total amount of bleeding during labor, the duration of the first and second stages of labor, and the length of postpartum hospitalization were summarized. It was found that the total amount of bleeding increased, and the length of hospitalization was longer in the painless delivery group, but there was no significant difference between the two groups. The duration of the first and second stages of labor in the painless delivery group were significantly prolonged. These results further support previous literary reports [16, 17]. Other studies also found that early epidural analgesia use in labor (when the cervix is less than 4.0 cm dilated) resulted in faster delivery compared to initiating the epidural later in labor [18, 19]. A recent meta-analysis did not find an association between low-concentration epidural analgesia and the duration of labor, but this meta-analysis is based on small trials of low quality [20]. These conflicting results may be due to different methodologies and how the labor onsets define the timing for initiating the epidural.
The neonatal outcomes are usually assessed by Apgar scores, and there was no significant difference in painless and non-epidural groups. This is in line with other studies that showed no difference in Apgar scores in epidural analgesia and no analgesia groups [21 ~ 23]. However, neonates with good Apgar scores still have a risk of neonatal acidaemia and adverse outcomes [24]. Both pH and BE values can be used to assess fetal metabolic acidosis during delivery. Umbilical cord blood pH is an important outcome indicator in obstetrics. Low arterial umbilical cord pH is closely related to the neonatal mortality (hypoxic-ischemic encephalopathy, seizures, intraventricular hemorrhage, periventricular leukomalacia, and cerebral palsy) incidence rate [25]. In normal healthy fetuses, a slight decrease in pH may not have clinical significance, but for fetuses with predisposing factors, even a slight decrease in pH may cause adverse neurological sequelae [26]. The present study did not find significantly low umbilical cord pH values in the epidural analgesia delivery group. However, some neonates with a normal pH at birth might still develop a hypoxic condition [27, 28]. The pCO2 of umbilical vein blood in the painless delivery group was significantly higher than that of the non-epidural delivery group, which may be related to the decrease of transitional ventilation caused by pain relief. In this study, the lactate, pCO2, and HCO3 - of umbilical artery blood - were significantly higher in the epidural analgesic delivery group than those of the non-epidural delivery group, which was consistent with previous reports, suggesting that the painless delivery group may increase the level of anaerobic metabolism due to the prolonged labor process, and the pain relief is also lower in pH, which requires the body to use reserve alkali, resulting in lower BE and HCO3-.
Although the present study shows that the pH slightly decreased, it did not reach a significant level, while the lactate level was significantly increased in the painless delivery group compare to the non-epidural group. Both lactate and pH values have been reported to be the best indicators of neonatal oxygenation index and acid-base status, and lactate has the most robust discrimination [29]. Two extensive studies on 2554 [24] and 1709 [25] neonates of singleton deliveries proved that the lactate of the umbilical artery has higher sensitivity and specificity for fetal asphyxia at delivery than that with the pH and base excess. Westgren et al. (1995) [30] analyzed 4045 cord samples and demonstrated that within the 1 minute Apgar score, the difference between pH value and lactate was the largest. For the Apgar score at 5 minutes, lactate was the best identification index. The sensitivity, specificity, positive, and negative predictive value of lactate in morbidity and mortality are comparable to pH and base deficits. Lactate significantly correlated with fetal pH, hemoglobin, base deficiency, pCO2, and HCO3-. Although pH is more often used as an indicator of neonatal disease than lactate in clinical practice, more blood samples and sophisticated equipment are required to measure pH and base excess than that required of measuring lactate; thus, the lactate measurement has a lower cost and is easier to maintain[31]. Epidural anesthesia results in transient uterine-placental dysfunction due to maternal and infant body temperature rise, which leads to a decrease in fetal tissue oxygen supply. When maternal vascular resistance decreases, it can reduce maternal systolic blood pressure. The lower blood pressure may result in uterine placental dysfunction and increase lactate level in neonatal tissues [32.]
There were some limitations to the present study. Firstly, the sample size is relatively small; a larger number of subjects could increase the strength of the results in a future study. Secondly, our results may be affected by confounding factors that were not collected, as we were unable to collect essential results such as anesthesia levels and subjective pain scores during labor. Thirdly, the subjective evaluation of cervical dilatation by obstetricians of differing experiences may differ, which may affect the actual evaluation of the duration of labor. Fourthly, although nurses strictly define the indications of umbilical cord blood collection, there are some differences between individual nurses in clinical practice. Finally, the present study only observed short-term (1 and 5 min Apgar score) neonatal outcomes; the long-term outcome needs to be investigated in the future.