This prospective randomized trial was held from January 2006 to January 2009 in the labor and delivery ward of the department of Obstetrics and Gynecology at Ha'Emek Medical Center in Afula, Israel, a university teaching hospital.
Women at term (gestational age of 37 weeks or more) with intact amniotic membranes and a singleton fetus in cephalic presentation, who had a spontaneous onset of labor, a cervical dilatation between two and four cm, vertex level of no more than two cm above the pelvic inlet and had a prolonged latent phase of labor were included in the study. Gestational age was confirmed by either a documented first trimester ultrasound or by known regular last menstrual period and a documented ultrasound in the second trimester.
The latent phase was defined as the interval between the start of regular contractions (women's report) combined with any cervical dynamics (dilatation and/or effacement) until the active phase of labor was established when cervical dilatation was greater than four cm. A prolonged latent phase was defined as lasting more than 20 hours for primiparous women and 14 hours for multiparous women .
Women with a previous uterine scar, rupture of membranes, placental abruption, severe preeclampsia, suspected fetal macrosomia (greater than 4000 g), a non-reassuring fetal heart rate tracing or any contraindication for a trial of labor, were excluded. Women who had a malformed fetus diagnosed in the antepartum period or had an antepartum fetal death were also excluded.
Women with the diagnosis of prolonged latent phase were randomly allocated to amniotomy (group 1), oxytocin (group 2) or both (group 3). Amniotomy in group 1 was performed immediately after admission to the delivery ward. If no progress in cervical dilatation was documented after two hours or there were fewer than three contractions in ten minutes recorded after one hour, oxytocin was added. In group 2, oxytocin was started immediately after admission to the delivery ward. If no progress in cervical dilatation was documented after two hours or there were fewer than three contractions in ten minutes recorded after 1 hour, amniotomy was performed. Group 3 had both amniotomy and oxytocin performed and started simultaneously after admission to the delivery ward. The protocol of oxytocin administration was one mU/min increased by one mU/min every 20 minutes until five contractions in ten minutes or cervical progress was documented. When no progress was documented after two hours despite five contractions in ten minutes, an internal pressure catheter was inserted and oxytocin was increased until a Montevideo score of 200 to 300 was achieved.
Randomization of the three groups was performed in blocks of ten using a computer randomization sequence generation program. The sequence was concealed until intervention was assigned.
Women who were admitted in the latent phase of labor to our labor ward and who progressed spontaneously without intervention composed the control group (group 4). The control group was selected by choosing the women who met the inclusion criteria during the study period. The purpose of selecting this group of women is to compare the duration of the different labor stages among the study groups to a spontaneously progressing women who did not need labor augmentation.
The primary outcome was the duration of time from initiation of labor augmentation until delivery. Women who were operated were excluded from the analysis of the primary outcome. Secondary outcomes were active phase duration, duration of first and second stages of labor, mode of delivery, maternal fever, antibiotic administration, postpartum hemorrhage, anal sphincter tears, Apgar score and maternal satisfaction.
Women expressed their satisfaction using a score from one (absolutely not satisfied) to five (absolutely satisfied). The following variables were considered: maternal age, ethnicity, parity, antepartum obstetric complications (gestational diabetes, hypertension, antepartum bleeding, thrombophilia, and oligohydramnios), epidural use, number of vaginal examinations, intra-partum fetal scalp-electrode or uterine pressure catheter use and birth weight.
Continuous electronic fetal heart rate monitoring for all groups was initiated and continued until delivery. Arrest of dilatation during the active phase was determined when the Montevideo score was between 200 and 300 for more than two hours. Arrest of descent was defined as an arrest of descent of the fetal head for more than one hour during the second stage of labor. When arrest of descent was diagnosed at a level below the midpelvis, a vacuum extraction was used, and when above the midpelvis, a cesarean delivery was performed. All groups were given standard care according to departmental guidelines when it came to midwifery support, i.e. 1 midwife per 1 to 2 laboring women and access to pain relief, i.e. epidural, intravenous pethidine and/or inhalation of a mixture of O2 with N2O according to maternal demand regardless of the measured cervical dilatation.
The study was approved by the local institutional review board and each woman signed an informed consent.
One way ANOVA or a Kruskal Wallis test in the case of non-normally distributed variables was performed to compare the continuous data of the four groups of women. Chi-square or Fisher exact tests when appropriate were used to compare the categorical data. Bonferroni post hoc tests in the case of normally distributed data or Mann-Whitney pair-wise comparisons with p < 0.05 considered to be significant. In the case of non-normally distributed data, Kruskal-Wallis test was used to determine pair-wise differences among statistically significant and borderline statistically significant variables. This analysis was repeated for primiparous and for multiparous women.
Mean time interval from initiation of augmentation until delivery was eight hours (+ 120 minutes), based on previous observation at our delivery ward. Accordingly, in order to demonstrate a difference of one hour between group three compared to group one and two with an alpha of 0.05 and a power of 90%, a sample size of 63 women per group was required. The primary analysis was performed on the groups as allocated, that is, by the intention to treat, including all women as randomized.