Approximately 8% of women with pregnancies at term have prelabor rupture of membranes (PROM). Management options include immediate induction of labor and observation in the hope that spontaneous labor will begin. Before 1996, some clinicians considered expectant management to be preferable for women because studies suggested the risk of cesarean delivery might be lower.1,2 The Term Prelabor Rupture of the Membranes (TermPROM) Study Group compared immediate induction with intravenous (IV) oxytocin or vaginal prostaglandin (PG) E2 gel, to expectant management up to 4 days followed by labor induction if labor did not begin spontaneously.3 There was no difference in the rate of cesarean delivery between the induction and expectant management groups.
We did this secondary analysis of data from the TermPROM Study to determine which factors independently predict cesarean delivery in women with PROM at term. Variables under consideration included parity, maternal age, duration of the latent period, spontaneous versus induced labor, duration of active labor, cervical dilation and effacement at study entry, development of clinical chorioamnionitis, previous cesarean delivery, use of oxytocin in labor, epidural anesthesia, internal fetal heart rate (FHR) monitoring, meconium staining, birth weight, gestational age at study entry, and country of birth. We also wished to determine whether there was significant interaction between mode of labor onset (induced versus spontaneous) and the duration of the latent period with regard to cesarean delivery.
Materials and Methods
The TermPROM Study, completed and reported on in 1996,3 involved 5041 women with singleton, term pregnancies and PROM from 72 institutions, in six countries. Rupture of membranes was determined clinically and confirmed by positive nitrazine or fern test. Women were excluded if they were in active labor, there had been a previous failed attempt to induce labor, presentation was noncephalic, or there was a contraindication to either induction of labor (eg, placenta previa) or expectant management (eg, maternal fever, meconium staining, or other evidence of maternal or fetal compromise). Women were assigned by a centrally controlled telephone randomization program to one of four treatments: immediate induction of labor with IV oxytocin, immediate induction of labor with vaginal PGE2, expectant management followed by induction of labor with IV oxytocin if necessary, and expectant management followed by induction of labor with vaginal PGE2 gel if necessary. If labor was induced with an infusion of oxytocin, the rate was titrated to contractions according to local hospital policy. If labor was induced with vaginal PGE2 gel, 1–2 mg was inserted into the posterior vaginal fornix, and this was repeated 6 hours later if labor had not started. Oxytocin was infused 4 hours later if labor still had not started. The details of the study design were published previously.3 The medical personnel made other decisions concerning fetal and maternal care and mode of delivery.
Approximately 95% of women in all groups had vaginal or introital cultures performed for group B streptococcus at study entry. Vaginal examinations were avoided, as part of the protocol, to minimize risk of ascending infection. If a digital or speculum vaginal examination was done before the study, information on dilation and effacement was recorded. Information on cervical dilation and effacement otherwise was not recorded before induction of labor or at the onset of spontaneous labor. For women in either of the induction groups, the cervical status at study entry most likely represented the status of the cervix before induction of labor, because labor was induced shortly after randomization. For the others, the state of the cervix might have become more favorable as time passed. Labor was considered to have begun when the cervix became dilated to at least 3 cm or effaced to at least 80% and when uterine contractions were occurring at least every 5 minutes. Clinical chorioamnionitis was considered present when one or more of the following criteria were met: maternal temperature persistently above 37.5C on two or more occasions, at least 1 hour apart, or a single temperature above 38C before delivery; maternal white blood cell count greater than 20,000 cells/mm3; or foul-smelling amniotic fluid.
Of the 5041 enrolled women, we excluded 13 who had prelabor cesarean deliveries. Among the 5028 remaining women, 4532 (90.1%) delivered vaginally and 496 (9.9%) by cesarean. Variables possibly affecting the need for cesarean delivery among normally laboring women were identified, and the association between those variables and mode of delivery was tested using univariate analyses (χ2 test). The variables associated with cesarean delivery at P ≤ .3 on univariate analysis and those variables for which there was previous evidence for an association with cesarean delivery were considered for the multivariate regression model. Because vaginal examinations were avoided in the Term-PROM Study, there was a substantial amount of missing data on cervical dilation and effacement; thus those variables were not considered for the model. Instead, we combined cervical dilation and effacement, with mode of labor onset, as one variable (induced labor with an unfavorable cervix or induced labor with a favorable cervix versus spontaneous labor), and that variable, regarding which information was available for 4113 women, also was considered for the model. An unfavorable cervix was defined as a cervix dilated less than 3 cm and effaced less than 80%.
The interaction term (induced versus spontaneous labor by duration of the latent period) was considered for the model. Multivariate analysis was done by stepwise logistic regression to determine the statistically significant (P < .05) independent predictors of cesarean delivery. Logistic regression analysis is a statistical method for evaluating the effects of multiple independent variables on a dichotomous dependent variable such as mode of delivery. The purpose of presenting the results of the univariate and multivariate analyses is to demonstrate the extent to which the effect of each independent variable was affected by the others.
The demographic information at study entry and perinatal outcomes, by country of birth, for the study population are detailed in Table 1. On univariate analysis, the variables that were significantly (P < .001) associated with an increase in cesarean delivery were birth weight of at least 4000 g; nulliparity; meconium staining; induced labor; use of oxytocin in labor; internal FHR monitoring; epidural anesthesia; clinical chorioamnionitis; duration of latent period of at least 12 hours; duration of active labor of 6–12 hours, versus less than 6 hours, and of at least 12 hours, versus less than 6 hours; induced labor with an unfavorable cervix at study entry, versus spontaneous labor; and delivery in Canada, versus Israel. Variables significantly (P ≥ .001 and ≤ .3) associated with an increase in cesarean delivery were cervical dilation of less than 3 cm at study entry (P = .015), previous cesarean delivery (P = .132), maternal age of at least 35 years (P = .135), and delivery in Canada, versus Sweden (P = .10), Denmark (P = .221), and the United Kingdom (P = .30). The variables not significantly (P > .3) associated with cesarean delivery on univariate analysis were delivery in Australia, versus Canada (P = .67); induced labor with a favorable cervix, versus spontaneous labor (P = .96); cervical effacement of less than 80% at study entry (P = .394); and gestational age of at least 41 weeks (P = .305).
All variables, other than cervical dilation and effacement, were considered for the multivariate regression model. On multivariate analysis, the strongest predictor of cesarean delivery among women with PROM at term was country of birth (Table 2). Women in Israel were significantly less likely to deliver by cesarean than were women in Canada (odds ratio [OR] 0.34; 95% confidence interval [CI] 0.15, 0.81), and women in Australia were significantly more likely to deliver by cesarean than were women in Canada (OR 1.93; 95% CI 1.29, 2.88). Other strong (OR greater than 2.5) predictors of cesarean delivery were nulliparity (OR 2.81; 95% CI 1.95, 4.05); duration of active labor exceeding 12 hours, versus less than 6 hours (OR 2.78; 95% CI 2.01, 3.85), previous cesarean delivery (OR 2.75; 95% CI 1.46, 5.16) and epidural anesthesia (OR 2.66; 95% CI 1.94, 3.65) (Table 2). Other less strong but statistically significant predictors were clinical chorioamnionitis; internal FHR monitoring; birth weight of at least 4000 g; use of oxytocin in labor; duration of active labor of 6–12 hours, versus less than 6 hours; latent period of at least 12 hours, versus less than 12 hours; and meconium staining (Table 2). Gestational age at study entry, induced versus spontaneous labor, and induced labor with an unfavorable cervix or a favorable cervix versus spontaneous labor were not associated with cesarean delivery on multivariate analysis. There was no significant interaction between duration of latent period and induced versus spontaneous labor.
Much of the debate surrounding PROM at term has centered around whether induction of labor increases the risk of cesarean delivery. The TermPROM Study and meta-analyses of randomized controlled trials have not found a statistically significant difference in the rate of cesarean delivery between induction of labor with oxytocin or PGs and expectant management.3–7 Despite those results, we thought it appropriate to explore further the association between induced or spontaneous labor and cesarean delivery. After controlling for other fetal and maternal factors for which we had information, we did not find induced labor to be associated with a higher risk of cesarean delivery, regardless of duration of the latent period and status of the cervix at study entry.
For women with PROM at term but otherwise without complications, the independent fetal and maternal risk factors for cesarean delivery were nulliparity, prolonged labor, previous cesarean delivery, epidural anesthesia, clinical chorioamnionitis, use of internal FHR monitoring, larger infants, use of oxytocin in labor, older maternal age, longer duration of latent period, and meconium staining. Except for duration of latent period, those risk factors are similar to those associated with cesarean delivery in women at term without PROM.8–10 The association between duration of latent period and cesarean delivery might be due to subclinical chorioamnionitis, because the effect was independent of the development of clinical chorioamnionitis and we previously found longer latent periods to be associated with increased risk of clinical chorioamnionitis.11
We found that country of birth was a strong predictor of cesarean delivery, after controlling for fetal and maternal factors. Variations in rates of cesarean delivery were noted previously among countries, institutions, and physicians and nurses.8,12–15 In 1991–1992, the rates of cesarean delivery in community hospitals, without facilities for neonatal intensive care, in Ontario, Canada, varied from 6.6 to 30.3%.13 Those large variations in rates of cesarean delivery for different settings likely are due to differences in environmental factors including variations in quality and degree of supportive care provided to women in labor, supervision of labor and birth by midwives versus physicians, timing of admission to labor and delivery units, use of fetal scalp sampling or interpretation of FHR monitor tracings to diagnose unreassuring FHR, routine versus selective use of epidural anesthesia, availability of practitioners with expertise in operative vaginal delivery, and accepted upper limits for length of first and second stages of labor, all of which can have an effect on the likelihood of cesarean delivery.16–22 It is not known specifically why Israel had a significantly lower rate of cesarean delivery than Canada, but this merits further investigation.
This study was a retrospective analysis of data, so there might be other fetal and maternal factors associated with cesarean delivery after PROM concerning which we had no or inadequate information. We had no information on environmental factors other than country of birth. Future prospective research should involve evaluation of changes in environment, while controlling for fetal and maternal factors. The ongoing Nursing SCIL Trial, funded by the National Institutes of Health, coordinated in Toronto by EDH, is an example of such an evaluation. The Nursing SCIL Trial is a multicenter, randomized controlled trial evaluating the effect of continuous, supportive care in labor by nurses in institutions in the United States and Canada.
The present study confirmed that the fetal and maternal risk factors for cesarean delivery for women with PROM at term are similar to those for women with other uncomplicated term pregnancies. After country of birth was controlled for, the greatest risks were for nulliparous women, those with long labors, those who had previous cesarean deliveries, and those receiving epidural anesthesia. The risk, however, was not increased if labor was induced. An approach that decreases the duration of the active phase of labor and the use of epidural anesthesia, particularly among nulliparous women, might decrease the rate of cesarean delivery in women with PROM at term.
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