Discontinuing oxytocin stimulation in the later stages of induced labor might lead to a slightly increased risk of cesarean section (C-section); however, it may also reduce the risk of dangerous pregnancy complications, researchers found.
Approximately 25% of labors are induced, and oxytocin is often administered to stimulate contractions. The problem with oxytocin, Sidsel Boie, MD, of Randers Regional Hospital, Randers, Denmark, and colleagues explained, is that there is a fine line between progressing labor and causing uterine hyperstimulation—defined as more than five contractions in 10 minutes—and abnormal fetal heart rate.
Previous research suggested that labor will continue if oxytocin stimulation is stopped once active labor begins, lowering the risk of C-section and avoiding the issue of uterine hyperstimulation—however, study limitations prevented these trials from confirming the effect of oxytocin stimulation.
Boie and colleagues conducted the “Continued versus Discontinued Oxytocin stimulation in the active phase of labor” (CONDISOX) trial to determine whether discontinuation of oxytocin stimulation once the active phase of induced labor is achieved reduces the overall rate of C-section. They published their findings in The BMJ.
“This double-blind, randomized, multicenter trial found that, in a setting where monitoring of the fetal condition and the uterine contractions can be guaranteed, a policy of discontinuation of oxytocin may lead to a small increase in the risk of caesarean section,” Boie and colleagues found. “On the other hand, the risk of uterine hyperstimulation and abnormal fetal heart rate was significantly reduced when oxytocin was discontinued, and this may be important in settings where close observation of mother and fetus may be challenging owing to shortages of resources. Other maternal and neonatal outcomes, including the women’s birth experience, did not differ significantly between the groups.”
For this study, Boie and fellow researchers recruited participants from nine delivery wards in Denmark and one ward in the Netherlands. Women were eligible for participation if they “had a singleton live fetus with a cephalic presentation at term and were stimulated with oxytocin for elective induction of labor or following spontaneous pre-labor rupture of membranes without progression in labor.” Patients were excluded if they were under 18 years of age, required an interpreter to understand the information material, had multiple pregnancy, had more than one previous serious C-section, had more than 4 cm of cervical dilation at the time of oxytocin infusion, had fetal heart rate abnormalities before oxytocin infusion, or had an estimated fetal weight of more than 4,500 g.
Patients received an intravenous infusion of 10 IU oxytocin diluted in 1,000 mL of isotonic saline (Denmark) or 5 IU oxytocin diluted in 50 mL of isotonic saline (Netherlands) starting at 3.3 mIU/min, which was increased every 20 minutes by 3.3 mIU/min until they achieved three to five contractions every 10 minutes. Women were randomized at the start of the active phase of labor—ruptured membranes with complete effacement of the cervix, cervical dilation of at least 6 cm, and at least three contractions every 10 minutes—to either continue receiving oxytocin at the standard concentration or receive placebo with saline.
Slow labor progress in the first stage of labor was defined as cervical dilation of less than 2 cm every four hours despite three to five uterine contractions in 10 minutes and/or after reaching the maximum infusion dose (30 mIU/min in Denmark, 33 mIU/min in the Netherlands); slow labor progress in the passive second stage was defined as “descent of the presenting part not reaching 2 cm below the ischial spines within three hours,” and in the active second stage as delivery not being achieved within two hours of maternal expulsive effort. Women who met these criteria were switched from the study medication to open label oxytocin infusion at a starting dose rate of 3.3 mIU/min.
The study’s primary outcome was delivery by C-section. A total of 1,200 women participated in the trial—607 were assigned to oxytocin discontinuation and 593 to continuation of infusion.
“The rates of caesarean section were 16.6% (n=101) in the discontinued group and 14.2% (n=84) in the continued group (relative risk 1.17, 95% confidence interval 0.90 to 1.53),” the study authors reported. “In 94 parous women with no previous caesarean section, the caesarean section rate was 7.5% (11/147) in the discontinued group and 0.6% (1/155) in the continued group (relative risk 11.6, 1.15 to 88.7),” reported Boie et al.
They also found that oxytocin discontinuation was associated with “longer duration of labor (median from randomization to delivery 282 vs 201 min; P<0.001), a reduced risk of hyperstimulation (3.7% vs 12.9%; P<0.001), a reduced risk of fetal heart rate abnormalities (27.9% vs 40.8%; P<0.001),” and similar rates of other adverse maternal and neonatal outcomes.
Boie and colleagues also noted that several women in both study groups stopped the study medication—311 (51.2%) in the discontinuation group and 197 (33.3%) in the continued group (P<0.0001). Reasons for discontinuation included slow labor progression in accordance with protocol, slow labor progression not in accordance with protocol, uterine techysystole or fetal heart rate abnormalities, or other (pyrexia, meconium stained amniotic fluid) not in accordance with protocol. In cases where slow labor progress was cited as the reason for stopping, all women were put on open label oxytocin.
While the study authors pointed to their trial’s organization, multicenter nature, double blind design, and large sample size as strengths of the analysis, they also acknowledged several limitations to their study, including the relatively high proportion of participants who discontinued the study medication; a “general impatience” with slower than average rates of cervical dilation among birth attendants, leading to “pressure from medical and midwifery colleagues to restart oxytocin,” even though the trial criteria had not been met; and a possible lack of generalizability to centers that use other methods of birth induction or other oxytocin stimulation regimens.
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Discontinuing oxytocin stimulation during the active phase of labor increased women’s risk for delivery by cesarean section, but it also reduced the risk for uterine hyperstimulation and abnormal fetal heart rate.
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Stopping uterine stimulation early may improve pregnancy outcomes in settings where close observation of mother and fetus may be challenging owing to shortages of resources.
John McKenna, Associate Editor, BreakingMED™
The study authors had no relevant relationships to disclose.
Cat ID: 41
Topic ID: 83,41,791,730,41,192
