epidural and the duration of labor

Epidural and the duration of labor

Epidural causes slight increase in the duration of the second stage of labor. There is no evidence that this prolongation causes adverse effects in newborns.

For practical purposes labor is divided into three stages. During the first stage the uterus develops contractions that push the fetus against the cervix of the uterus and gradually force it to open. The degree of cervical opening reflects progress of labor during this stage. The second stage starts when uterine cervix is fully dilated and the woman begins to actively push. The result of this stage is birth of the child. In the next, third stage of labor, the uterus contracts further and expels the placenta.

It has been observed that in some instances epidural prolongs labor. This has been confirmed by the results of the latest Cochrane review on the effects of labor epidurals that stated that while epidural has no effect on the first stage of labor, it prolongs the second stage.

The potential significance of the prolongation of the second stage of labor is obvious. The second stage is the most stressful time for the neonate, the time when the fetus is propelled through the tight birth canal and is subjected to the mechanical stress. During this stage the umbilical cord can become compressed between the body of the neonate and anatomical structure of the mother, resulting in impaired blood supply to the baby with possible development of hypoxia and consequent complications which, at least in theory, may be severe. Impaired progress of labor during second stage may necessitate the use of forceps or vacuum, which are associated with significant complications such as perineal tears and neonatal trauma.

Data from clinical practice, however, presents less dramatic reality. Recently updated Cochrane Database review looking into the effects of labor epidural shows that this prolongation is modest, about fifteen minutes. In spite of second stage being slightly longer no adverse effects were observed in epidural groups. There was no difference in the number of newborn babies who had Apgar scores below 7 at five minutes after birth between epidural and non-epidural patients, and when several technically flawed trials were excluded from the analysis there was even 44% reduction of this adverse effect in the epidural group, though not statistically significant. There were less neonates in the epidural group with umbilical cord blood pH lower than 7.2, the value used as a cut-off for diagnosing neonatal hypoxia. Among the newborns in the epidural group the need for the use of naloxone – opioid antagonist used to treat respiratory depression in neonates – was considerably lower. Overall, not only there was no indication that neonates suffer adverse effects from epidural analgesia, according to some parameters they were doing even better.

Labor is a complex process and its duration is determined by multitude of factors, as has been demonstrated by several recent trials.

The study published in 2007 analyzed the database of the Department of Obstetrics, Gynaecology and Reproductive Sciences of the University of California in San Francisco from 1980 to 2001 which included more than 30,000 patients in total. All patients were divided into groups according to their age, in increments of 5 years. The duration of the first and the second stages of labor increased progressively with age. Among nulliparous women the duration of the second stage of labor increased from 51 minutes among those who were younger than 20 years of age to 148 minutes in those over the age of 39. Similar increase was observed in multiparous women, though the magnitude was less dramatic: from 16 to 26 minutes. The analysys included other factors, such as the use of epidural, induction of labor, ethnicity, gestational age, Medicaid insurance status, birth weight, complicated position of the fetus, body mass index, cesarean delivery, year of delivery, and the presence of chorioamnionitis, inflammatory process in the placenta. In nulliparous women the induction of labor and the use of epidural prolonged second stage of labor. However the second stage in older nulliparous women in general was longer than in their younger counterparts, regardless of epidural status and whether labor was spontaneous or induced.

Earlier data analysis of 27,521 births in the same department focused on ethnicity and its possible effects on the duration of labor. While the first stage was not different between the groups, the second stage was considerably shorter among black women compared to White, Asian and Latina women, albeit modestly, about 22 minutes in nulliparas and 7 minutes for multiparas. In Asian women the second stage lasted longer.

Epidural technique may also affect the duration of labor. Two trials independently studied the effects of walking epidurals on the outcomes of labor, including its duration. One of them found statistically significant difference was noted in the duration of labor: 173.4 (+/-109.9) in epidural vs. 236.4 (+/-130.6) minutes in non-epidural group. The other found no such shortening of labor by epidural, as measured from the time of epidural insertion to complete cervical dilatation. The studies used different local anesthetic mixtures: 0.1% ropivacaine and 0.6 mcg/ml sufentanyl in the former and much weaker mixture, 0.07% ropivacaine and 2 microgram/ml of fentanyl in the latter. It is plausible that the level of analgesia produced by less potent mixture in the second study was not adequate to shorten labor. It is equally possible that other factors that were not taken into account in both studies influenced the duration of childbirth.

It has also been demonstrated that epidural placed early in labor may have different effect on the duration when compared with late epidural. In a 2009 study from Chicago labor epidural was placed either before or after cervical dilation reached 4cm. There was no difference in the rate of caesarean section, mode of vaginal delivery or neonatal Apgar scores between the groups. On the other hand, pain scores were considerably lower and the duration of labor shorter in the early epidural group.
Labor is a complex process, and the duration of its stages varies greatly from patient to patient, independently of the use of epidural. The woman’s age remains the most important parameter that determines the duration of childbirth. The present consensus is that epidural analgesia increases the duration of the second stage of labor. The data from other trials suggest that superior pain relief resulting from epidural may actually shorten labor. In any case, the increase that has been demonstrated is modest and clinically not significant. The main concern of prolonged labor is the wellbeing of the newborn. However, no neonatal side-effects have been demonstrated as the result of longer labor caused by epidural.

References:

1. Anim-Somuah M, Smyth RMD, Howell CJ. Epidural versus non-epidural or no analgesia in labour. Cochrane Database of Systematic Reviews 2005, Issue 4. Art. No.: CD000331. DOI: 10.1002/14651858.CD000331.pub2.

2. Greenberg MB, Cheng YW, Sullivan M, Norton ME, Hopkins LM, Caughey AB. Does length of labor vary by maternal age? Am J Obstet Gynecol 2007;197:428.e1-428.e7.

3. Greenberg MB, Cheng YW, Hopkins LM, Stotland NE, Bryant AS, Caughey AB. Are there ethnic differences in the length of labor? American Journal of Obstetrics and Gynecology (2006) 195, 743–8.

4. Karraz MA. Ambulatory epidural anesthesia and the duration of labor. Int J Gynaecol Obstet. 2003 Feb; 80(2): 117-22.

5. Vallejo MC, Firestone LL, Mandell GL, Jaime F, Makishima S, Ramanathan S. Effect of epidural analgesia with ambulation on labor duration. Anesthesiology. 2001 Oct; 95(4): 857-61.

6. Wong CA, McCarthy RJ, Sullivan JT, Scavone BM, Gerber SE, Yaghmour EA. Early compared with late neuraxial analgesia in nulliparous labor induction: a randomized controlled trial. Obstet Gynecol. 2009 May;113(5):1066-74.

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Dr. Eugene Smetannikov is a practicing anesthesiologist with the interest in obstetric anesthesia. He is the author of the most comprehensive book on the subject, The Truth About Labor Epidural