The results “suggest that the high-dose oxytocin may be more important in preventing cesarean section than the actual timing of the oxytocin intervention,” the researchers said.
They claim that one cesarean section could be prevented for every 50 women treated with high-dose instead of low-dose oxytocin.
And even though the high-dose regimen nearly doubles the risk of hyperstimulation, results showed no harm to mothers or babies, the investigators reported in their paper, published online May 10 in the American Journal of Obstetrics & Gynecology.
Senior author Dr. William D. Fraser, from Universite de Montreal, Canada, and his colleagues conducted a literature search for randomized controlled trials in pregnant women in spontaneous labor and without prior use of oxytocin.
They defined high-dose as starting with at least 4 mU/min and continuing in increments of at least 4 mU/min. Low-dose regimens involved initial doses of 1-4 mU/min with increments of 1-2 mU/min.
Their search turned up 10 trials involving 5423 women. Maximum oxytocin infusion rates ranged from 4-90 mU/min in the high-dose group (n = 2748) and from 1-31.7 mU/min in the low-dose group (n = 2675).
There were 361 cesarean sections (13.1%) in the high-dose group and 405 (15.1%) in the low-dose group (risk ratio 0.85).
In seven trials, the high dose significantly increased the rate of spontaneous vaginal delivery from 65.6% to 70.1% (RR = 1.07).
Five trials showed that increasing the dose significantly shortened the mean labor interval by 1.54 hours, and three showed that the proportion of women with labor lasting more than 12 hours was cut in half (RR 0.46).
In five trials, hyperstimulation occurred in 20.4% of high-dose patients and 10.5% of low-dose cases (RR 1.91). Hyperstimulation had no effect on fetal heart rate, fetal distress, or neonatal morbidity indicators, however.
High-dose augmentation did not affect use of epidural analgesia, postpartum hemorrhage, uterine atony or rupture, or shoulder dystocia.
The authors do note the possibility that high-dose oxytocin could increase labor pain, but there was no documentation of this in the studies. Their analyses were also limited in that most of the trials were not blinded. Perhaps more importantly, the decision criteria for cesarean section were not standardized.
The authors advise clinicians to consider medical history, parity, and indicators of maternal and fetal well-being when planning oxytocin augmentation. Furthermore, they should inform women of the potential benefit on cesarean section rates as well as possibly increased discomfort.
Am J Obstet Gynecol 2010.