New Analgesia Techniques For Labor Raise Chances Of Normal Vaginal Birth

Two alternatives to traditional epidural analgesia effectively reduced pain during labor and, moreover, increased the likelihood that women would have a normal vaginal delivery in a randomized controlled trial conducted in the United Kingdom.1 Whereas 35% of women who were given a traditional epidural had a normal delivery, the proportion was significantly higher--43%--among women who received either of two newer types of pain relief that combine an opioid with a reduced concentration of the local anesthetic. The alternative techniques' benefits for delivery, however, were somewhat offset by the possibility that they have adverse effects on a small proportion of newborns.

Between February 1999 and April 2000, researchers at two maternity units randomly assigned 1,054 nulliparous women who requested pain relief during labor to receive one of three types of analgesia: a traditional epidural; a low-dose solution administered by spinal injection and followed by intermittent delivery of additional epidural analgesia (combined spinal epidural); or the same low-dose mixture delivered through continuous infusion. Women receiving traditional or low-dose injections could request additional doses as the analgesia wore off. Detailed information about labor and delivery were gathered by the anesthetist and midwife attending each delivery, and through interviews with participants conducted within 48 hours after the birth.

Thirty-five percent of women who received a traditional epidural had a normal vaginal delivery, compared with 43% in each of the other groups; the differences were statistically significant. Instrumental vaginal delivery was required by 37% of women in the traditional epidural group, but by only 28-29% of those receiving low-dose alternatives; again, the differences were statistically significant. In all three groups, 28-29% of women delivered by cesarean section.

Slight variations in the characteristics of labor were noted among groups. The second stage of labor was more likely to be one hour or less for women who received a low-dose infusion (34%) than for those who had a traditional epidural (26%). Women in the infusion group also were more likely than those who had a traditional epidural to push for one hour or less (63% vs. 51%) and to say that they were able to push throughout labor (38% vs. 28%). In the postpartum interview, women in all three groups gave similar reports of the severity of pain they had experienced during labor.

Whereas a traditional epidural produces motor paralysis, the low-dose alternatives preserve muscle tone and permit women to remain mobile during labor. Thus, 30 minutes after receiving a low-dose combined spinal epidural or beginning low-dose infusion, the vast majority of women were able to flex their hips (89% and 80%, respectively), and about half (59% and 52%, respectively) could bend their knees; few were unsteady on their feet at this time. Nearly four in 10 women in both low-dose groups walked or stood during labor.

The researchers assessed the effects of the different regimens on newborns by comparing their Apgar scores five minutes after birth, need for resuscitation and rates of admission to neonatal intensive care units. Low Apgar scores (seven or less) were rare, and while differences were not statistically significant, the researchers point out that more infants in the low-dose groups than in the traditional epidural group scored in this range. Infants whose mothers had received a low-dose infusion were more likely than those whose mothers had a traditional injection to need high-level resuscitation efforts (5% vs. 1%), but rates of admission to intensive care units and the need for any resuscitation were similar for all three groups of infants.

According to the researchers, a number of mechanisms might explain why low-dose epidural techniques increase a woman's chances of having a normal vaginal delivery. The ability to walk during labor might, they note, aid the descent of the infant's head; the preservation of motor function also might help both "voluntary and involuntary maternal efforts to give birth" late in labor. Acknowledging that the benefits to women of low-dose epidural techniques must be weighed against "possible adverse effects" on a few infants, the researchers conclude that "continued routine use of traditional epidurals might not be justified."--D. Hollander


1. Comparative Obstetric Mobile Epidural Trial (COMET) Study Group UK, Effect of low-dose mobile versus traditional epidural techniques on mode of delivery: a randomised controlled trial, Lancet, 2001, 358(9275):19-23.