To the Editor:
We congratulate Wang et al .1for their single-institution, randomized controlled trial of 12,793 parturients. The investigators confirmed that nulliparas who receive neuraxial labor analgesia in early labor (defined in this study as cervical dilation ≥ 1 cm and < 4 cm) are not at greater risk for cesarean delivery or prolonged labor compared with nulliparas who wait until cervical dilation is more than or equal to 4 cm for initiation of neuraxial analgesia. These results are in agreement with similar smaller studies from our institution2,3and others.4
We would like to clarify one point. The authors state in the introduction that “current best available evidence in nulliparous women … supports that epidural analgesia is safe in laboring women with cervix dilated 2 cm or more” and cite our study2and that of Ohel et al .4to support this statement. In addition, they suggest that current data do not address the effects of neuraxial analgesia when cervical dilation is less than 2 cm. This statement is not correct. Both our studies2,3and the study by Ohel et al .4randomized women in early labor (cervical dilation < 4 cm) to neuraxial versus systemic opioid analgesia at the first request for pain relief, no matter the cervical dilation. Indeed, the median cervical dilation at initiation of analgesia was 2 cm in our studies,2,3and the mean dilation was 2.1 cm in the study by Ohel et al .,4meaning that 50% of the study populations had cervical dilation 2 cm or less at the initiation of analgesia. Therefore, we disagree with Wang et al . that data do not exist to support the practice of initiating neuraxial labor analgesia when cervical dilation is less than 2 cm.
We are also concerned about the reporting and interpretation of the data regarding one of the secondary outcomes, duration of labor.1The duration of labor and duration of neuraxial analgesia in the study by Wang et al . are significantly longer (hours) than that in our studies of spontaneous2and induced3labors, and in the study by Ohel et al .4with a mixed parity population. In table 2, the outcome of interest is listed as “Length of labor (from analgesia request to vaginal delivery), h§.”1However, in the footnote to the table, the symbol “§” is defined as the length of labor starting from the onset of regular uterine contractions to the time of delivery of the placenta. The text describing the results of the Kaplan–Meier duration of labor analysis indicates that duration was defined as the interval from analgesia request to delivery. However, it is unclear why the median duration of epidural analgesia is 12.6 h in the early (latent phase) neuraxial analgesia group (table 21); but, the median duration of labor from analgesia request is 627 min (10.5 h; fig. 2A1).
In our studies, we defined duration of labor as the time from analgesia request until delivery (∼7 h),2and Ohel et al .4defined the duration of labor as the time of randomization until delivery (∼6 h). This distinction is important for two reasons. First, the timing of the first regular contraction is hard to specify, and we suggest that pinpointing this time is subject to considerable bias. Second, both we2,3and Ohel et al .4found that the duration of labor was significantly shorter in women randomly assigned to early neuraxial compared with early systemic opioid analgesia, whereas Wang et al .1did not. We suggest that the investigators cannot ascertain the effect of early labor analgesia on duration of labor by using the time of onset of regular contractions as the start time of labor. The ill-defined and likely highly variable interval between onset of regular contractions and the actual therapeutic intervention (initiation of analgesia) may obscure any differences that may have occurred because of the intervention. To ascertain the effect of an intervention on the duration of labor, the start time must be close to the time of the intervention. Therefore, if duration of labor was defined as the interval between the onset of regular contractions and delivery, Wang et al .1cannot make valid conclusions about the effect of early neuraxial analgesia on the progress of labor. If the investigators defined the start time of labor as the time of request of analgesia, then there must be significant differences in labor progress between the American2,3and Israeli4populations of the previous studies and the current Chinese population,1in that labor was significantly longer in the Chinese population.
*Northwestern University Feinberg School of Medicine, Chicago, Illinois. c-wong2@northwestern.edu
