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Professor, Department of Obstetrics and Gynecology, University of Colorado School of Medicine, Aurora
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SYNOPSIS: A recent meta-analysis of randomized, clinical trials has shown that discontinuing oxytocin infusion once active labor has been attained in inductions and augmentations of labor will result in a reduction of cesarean delivery and tachysystole, but an increase in the length of labor.
SOURCE: Saccone G, Ciardulli A, Baxter JK, et al. Discontinuing oxytocin infusion in the active phase of labor: A systematic review and meta-analysis. Obstet Gynecol 2017;130:1090-1096.
The rate of induction of labor in the United States is about 23%.1 Since the uterus and cervix often are not ready for labor, it is not surprising that induction of labor is associated with an increased rate of cesarean delivery, which is now about 30%. Most often, the rationale for using oxytocin has been to initiate contractions and to assist in the transition into active phase. Oxytocin-driven tachysystole is not an uncommon (or innocuous) byproduct and can result in abnormal fetal heart rate patterns. This leaves one to wonder whether the labor medication is really needed once the uterus is on its own during the active stage of labor.
Saccone et al undertook a meta-analysis of randomized, clinical trials (RCTs) comparing a protocol of a “business-as-usual” approach of continuing oxytocin through delivery against one in which the infusion was stopped once the active phase was attained. They analyzed data from nine RCTs involving 1,538 pregnancies, all of which had inductions of labor or augmentations with oxytocin. In one group, the infusion was discontinued once active labor was achieved, but if labor arrested (as defined by a plateauing of cervical dilatation over two hours) then it was restarted. In the other group (controls), the oxytocin was continued, generally at the same dosage, until delivery. Only three of the studies employed placebo control. In all studies, the definition of active labor was cervical dilatation of
5 cm of greater.
The meta-analysis included 764 patients in the discontinuation group and 774 patients in the control (continuation) group. An average of 30% in the discontinuation group had to have oxytocin restarted because of an arrest in dilatation, and the oxytocin infusion was stopped because of “fetal distress” in 7.7% of the control group. The authors were aware of the potential biases in this type of study, and they addressed the seven domains of bias described in the Cochrane Handbook for Systematic Reviews of Interventions.2
The primary outcome measure was the cesarean delivery rate. The rate in the discontinuation group was 9.3% vs. 14.7% in the control group (relative risk [RR], 0.64; 95% confidence interval [CI], 0.48-0.87). Secondary outcomes included the rate of tachysystole, which was 6.2% vs. 13.1% (RR, 0.53; 95% CI, 0.33-0.38). The discontinuation group had an average active phase of labor that was 27.6 minutes longer than the control group (95% CI, 3.94-51.36 minutes). There were no significant differences in any of the other secondary variables evaluated.
In view of the high cesarean delivery rate, many common labor protocols have undergone re-evaluation. This has led to more liberal thresholds of tolerance for the lengths of active first and second stages of labor. Friedman’s original data suggested that the active phase started when patients had attained 4 cm of dilatation. In their recent labor guidelines,3 the American College of Obstetrics and Gynecology and the Society of Maternal Fetal Medicine increased the dividing line between the early and active phases of labor to 6 cm. Also, these guidelines indicate that providers should be more patient before considering intervention when progress in labor is sluggish. In fact, it was suggested that the label “arrest of labor” in the latent phase should not be used unless adequate contractions are attained for 12 to 18 hours following rupture of membranes and augmentation with oxytocin, if needed. Also, arrest of labor in the active phase now has been defined as no progress in dilatation after at least four hours of adequate contractions, thereby doubling the original threshold of two hours.
The concept of stopping oxytocin once adequate contractions have been attained in strength and frequency not only appeals to patients who wish to experience a more natural labor, but it also may have some scientific merit. Two studies have suggested that after about 10 hours of induction, the oxytocin receptors may not respond, and further infusion even could have the opposite effect on contractions.4,5
This meta-analysis has shown that the possible benefits from oxytocin discontinuation are lower rates of cesarean delivery and tachysystole. The downside is a longer length of labor, by an average of 27 minutes (or an addition of about eight to nine more contractions). Since the authors applied intention-to-treat methodology, the above data included the 30% in the discontinuation group whose infusion needed to be restarted.
Is there a drawback to this practice? Prolonged labor has been associated, in general, with a higher rate of amnionitis and shoulder dystocia.6 Authors of one of the RCTs found a nonsignificant trend toward a higher rate of amnionitis. However, this and shoulder dystocia were not addressed in the other papers in the meta-analysis. That concern will need further study.
The meta-analysis showed a 35% decrease in the cesarean delivery rate. When weighing the downside of an extra half hour of labor against a substantially lower chance of having a cesarean delivery, I would guess most patients would vote for stopping the oxytocin.