Objective
To estimate and compare the duration and progress of labor in women induced with misoprostol vs Foley catheter plus oxytocin.
Study Design
We performed a retrospective cohort study of labor progress among 617 consecutive term pregnancies induced with misoprostol (n = 503) or Foley catheter plus oxytocin (n = 114) who completed the first stage of labor. Labor duration and progress in the entire cohort, and stratified by parity, were compared in multivariable interval-censored regression models adjusting for maternal obesity and birthweight. Repeated-measures analysis with 9th degree polynomial modeling was used to construct average labor curves.
Results
Total duration of labor was not significantly different in women induced with misoprostol compared with the Foley catheter (median duration from 1 to 10 cm: 12 vs 14.2 hours, P = .19). Progress from 1 to 4 cm was more rapid with the Foley catheter (median: 3.4 vs 5.6 hours, P < .01), although progress from 4 to 10 cm was slower (median: 6.3 vs 3.6 hours, P < .01). Labor curves demonstrated transition from latent to active labor at about 4 cm cervical dilatation with misoprostol and at 6 cm for the Foley catheter. Similar general patterns were noted for nulliparous and multiparous women, except for a shorter duration of labor with the Foley catheter among multiparous women.
Conclusion
Induction of labor with the Foley catheter is associated with more rapid initial cervical dilation, but transition to active labor occurs later compared with misoprostol. These differences should be considered in the management of induced labor.
Induction of labor is frequently used in contemporary obstetrics and rates continue to increase. It is associated with increased risk of cesarean delivery, especially among women with an unfavorable cervix. This increased risk appears to be strongly influenced by the duration of the induction attempt. Yet there are no clear expectations of normal duration and course of induced labor. Using interval-censored regression analysis, we recently demonstrated that induced labor progresses slower than labor of spontaneous onset. However, the effect of different methods of labor induction on progress of labor has not been well characterized.
The Foley catheter and misoprostol are 2 common methods of labor induction in the United States when the cervix is unfavorable. The Foley catheter acts by mechanically dilating the cervix and releasing endogenous prostaglandins. Misoprostol, a synthetic prostaglandin E1, promotes biochemical remodeling of the cervix and triggers uterine contractions. Prior studies suggest both methods are effective for labor induction. However, data on their relative effects on the course of labor are limited. Prior studies assessing the course of labor in women induced with misoprostol or Foley catheter compared induction-to-delivery intervals. Such data are of limited value for the clinical management of labor where cervical dilatation is assessed intermittently and prospectively. Assessment of only induction-to-delivery intervals may obscure potentially important differences at different points in the labor course. For example, anecdotal evidence suggests women induced with the Foley catheter may not be in active labor even when the cervix is 3-4 cm or more dilated following expulsion of the Foley catheter. Establishing standards for onset of active labor in pregnancies induced with misoprostol or Foley catheter would potentially reduce the number of cesareans performed for failed induction of labor.
The objective of this study was to estimate and compare the duration and progress of labor in women induced with misoprostol or Foley catheter. Specifically, we sought to estimate onset of active labor in women induced with the 2 methods.
Materials and Methods
We conducted a retrospective cohort study of consecutive term, vertex singleton deliveries from 2004 to 2008 at a single academic teaching hospital. The study was approved by the Washington University School of Medicine Human Research Protection Office. Women were eligible if they underwent labor induction and completed the first stage. We excluded women if they had cesarean delivery in the first stage of labor, were in spontaneous labor on admission, or had a known fetal anomaly. Detailed demographic information was extracted from patients’ records including medical and surgical history, obstetric and gynecologic history and prenatal history. We abstracted detailed labor and delivery information including medications, labor onset type, indications for induction, method of labor induction, cervical examination times, cervical dilatation (0 to 10 cm), fetal head station (−5 to +5) and mode of delivery. Inductions of labor without any obstetric or medical indication as classified as elective. Pregnancies were dated by a woman’s last menstrual period and confirmed with first or second trimester ultrasonography using standard criteria. The comparison groups were defined by induction with misoprostol or the Foley catheter. We excluded women induced with a combination of misoprostol and Foley catheter or with another type of prostaglandin.
Labor and delivery care was provided largely by resident physicians under the supervision of attending physicians. However, per institutional obstetric protocols women with prior cesareans were not induced with misoprostol. The decision to use the Foley catheter or misoprostol was determined by the admitting physician. Cervical examinations were performed at regular intervals, usually every 2 hours. Women undergoing induction with misoprostol received 25 mcg vaginally every 4 hours until cervical ripening was achieved. Oxytocin was then started as needed, after at least 4 hours from when the last misoprostol was placed. Oxytocin was administered per standard institutional protocol starting at 2 milliunits per minute and increasing by 2 milliunits every 20 minutes until regular uterine contractions occurred. When the Foley catheter was used for induction, it was placed blindly or under direct visualization with the aid of a speculum. The balloon was inflated to 60 cc and the catheter was taped under traction to the woman’s thigh. Oxytocin was typically started at the same time and titrated until regular contractions occurred. The Foley catheter was examined periodically until it was expelled. Artificial rupture of membranes was performed once it was feasible.
We initially compared all women induced with misoprostol to those induced with the Foley catheter. All analyses were then further stratified into nulliparous and multiparous women. Univariable analysis was used to assess differences in baseline demographic and pregnancy characteristics. The χ 2 test or Fisher exact test was used for categorical variables as appropriate. Continuous variables were examined for normality using the Kolmogorov-Smirnov test. The Student t test was used for normally distributed continuous variables and the Mann-Whitney test was used for nonnormally distributed variables.
Median duration of labor and progress from 1 integer centimeter of cervical dilatation to the next (called traverse time) was estimated using interval-censored regression analysis with the assumption of log-normal distribution. This was necessary because cervical dilation is assessed intermittently and it is not possible to know exactly when cervical dilatation changed from 1 measure to another. Further, duration of labor is known to have a skewed distribution toward the left and generally fits a log-normal distribution. Thus, interval-censored regression with the assumption of log-normal distribution enabled us to estimate median traverse times from 1 integer cervical dilation to another together with 5th and 95th percentiles. We controlled for confounders using multivariable interval-censored regression models. Potential confounders were selected based on bivariate analysis. Statistically significant variables (maternal obesity and birthweight) were included in the final model.
We constructed average labor curves using repeated-measures analysis with 9th degree polynomial modeling. This involved taking the independent variable to sequential powers. A 9th order polynomial was the best fit for our cervical dilatation data. Repeated-measures analysis was required to take into account the correlation of multiple cervical examinations in the same women. Because achievement of complete cervical dilatation was known with certainty for all subjects in this cohort, we constructed labor curves starting at 10 cm cervical dilatation and worked backward. The resulting curves were then reversed.
Tests with P < .05 were considered significant. We included all patients meeting inclusion criteria during the study period; formal sample size estimation was not performed. Statistical analyses were completed using STATA version 11.1 (StataCorp, College Station, TX) and PROC LIFEREG of SAS 9.2 (SAS Institute, Cary, NC).
Results
Of 5388 consecutive women with singleton term pregnancies and vertex presentation who completed the first stage of labor during the study period (2004–2008), 617 were induced with misoprostol (n = 503) or Foley catheter (n = 114). For the entire cohort, women induced with misoprostol or the Foley catheter were comparable with regard to several demographic and pregnancy characteristics ( Table 1 ). Specifically, there were no significant differences in parity, race, indications for induction, and use of regional anesthesia. However, women induced with the Foley catheter had higher median Bishop score on admission and were more likely to require oxytocin augmentation. All women with prior cesareans were in the Foley catheter group.
| Characteristic | Misoprostol (n = 503) | Foley catheter (n = 114) | P value |
|---|---|---|---|
| Maternal age (y), mean (SD) | 24.7 (6.2) | 24.9 (6.4) | .81 |
| Maternal weight (kg), mean (SD) | 90.1 (21.1) | 86.1 (18.3) | .06 |
| Maternal BMI (kg/m 2 ), mean (SD) | 33.3 (7.5) | 32.6 (6.6) | .34 |
| Obese (BMI >30 kg/m 2 ), n (%) | 319 (64.7) | 65.0 (58.0) | .19 |
| Parity, n (%) | |||
| Nulliparous | 206 (41.0) | 38 (33.3) | .13 |
| Multiparous | 297 (59.1) | 76 (66.7) | |
| Maternal race, n (%) | |||
| Black | 323 (64.2) | 85 (74.6) | .06 |
| White | 129 (25.7) | 24 (21.1) | |
| Other | 51 (10.1) | 5 (4.4) | |
| Chronic hypertension, n (%) | 30 (6.0) | 7 (6.1) | .94 |
| Diabetes, n (%) | 14 (2.8) | 6 (5.3) | .18 |
| Smoking, n (%) | 80 (15.9) | 27 (23.7) | .05 |
| Alcohol use, n (%) | 4 (0.8) | 2 (1.8) | .35 |
| Indication for induction, n (%) | |||
| Elective | 152 (33.1) | 16 (24.2) | .41 |
| Oligohydramnios | 62 (13.5) | 11 (16.7) | |
| Maternal comorbidity | 51 (11.1) | 12 (18.2) | |
| Preeclampsia | 57 (12.4) | 6 (9.1) | |
| Nonreassuring fetal status | 39 (8.5) | 7 (10.6) | |
| Other | 98 (21.4) | 14 (21.2) | |
| Admission Bishop score, median (range) | 1 (0–7) | 3 (0–8) | < .01 |
| Admission cervical dilation, median (range) | 1 (0–2) | 1 (0–3) | < .01 |
| Gestational age (wks), mean (SD) | 39.1 (1.4) | 39.3 (1.3) | .41 |
| Prior cesarean, n (%) | 0 (0) | 24 (21.1) | < .01 |
| Fetal sex, n (%) | |||
| Male | 235 (46.8) | 61 (53.5) | .20 |
| Female | 267 (53.2) | 53 (46.5) | |
| Birthweight (g), mean (SD) | 3261.1 (560.6) | 3256.4 (519.0) | .94 |
| Macrosomia (birthweight >4000 g), n (%) | 5 (4.4) | 30 (6.0) | .51 |
| Oxytocin augmentation | 385 (76.5) | 99 (86.8) | .02 |
| Regional anesthesia | 466 (92.6) | 107 (93.9) | .65 |
Total duration of labor in the entire cohort by induction method was not significantly different (duration from 1 to 10 cm: 12.0 vs 14.2 hours, P = .19) ( Table 2 ). However, women induced with the Foley catheter progressed more rapidly from 1 to 4 cm (3.4 vs 5.6 hours, P < .01), and slower from 4 to 10 cm (6.3 vs 3.6 hours, P < .01). Analyses of centimeter to centimeter progress confirmed that dilations from 2 to 3 and 3 to 4 cm were more rapid in the Foley catheter group, although progress in centimeter increments was more rapid in the misoprostol group thereafter. Notably, times for progress from each cervical dilation to the next after 4 cm were significantly shorter in the misoprostol group. Labor curves for the entire cohort demonstrated transition from latent to active labor at approximately 4 cm cervical dilation for misoprostol and at approximately 6 cm for the Foley catheter ( Figure 1 ).
| Cervical dilation | Misoprostol | Foley catheter | P value a |
|---|---|---|---|
| From 1 to 10 cm | 12.0 (5.1, 28.0) | 14.2 (6.1, 33.2) | .19 |
| From 4 to 10 cm | 3.6 (0.9, 14.6) | 6.3 (1.6, 25.5) | < .01 |
| From 1 to 2 cm | 2.7 (0.6, 12.1) | 1.8 (0.4, 8.4) | .69 |
| From 2 to 3 cm | 1.4 (0.3, 7.9) | 0.8 (0.1, 4.3) | .03 |
| From 3 to 4 cm | 1.5 (0.2, 11.3) | 0.8 (0.1, 5.8) | < .01 |
| From 4 to 5 cm | 0.9 (0.1, 7.2) | 1.6 (0.2, 12.7) | < .01 |
| From 5 to 6 cm | 0.4 (0.04, 3.4) | 0.8 (0.1, 7.2) | < .01 |
| From 6 to 7 cm | 0.3 (0.03, 2.0) | 0.4 (0.1, 3.4) | < .01 |
| From 7 to 8 cm | 0.2 (0.03, 1.0) | 0.2 (0.03, 1.2) | .02 |
| From 8 to 9 cm | 0.2 (0.02, 1.0) | 0.3 (0.04, 1.7) | < .01 |
| From 9 to 10 cm | 0.2 (0.03, 1.3) | 0.2 (0.04, 1.4) | < .01 |
a Adjusted for obesity (body mass index >30 kg/m 2 ) and birthweight >4000 g.
In all, 265 nulliparous women were induced with misoprostol and 49 were induced with the Foley catheter ( Table 3 ). Nulliparous women induced with misoprostol and the Foley catheter were similar in several baseline characteristics. As observed for the entire cohort, the median Bishop score on admission was slightly higher in women induced with the Foley catheter. The indication for induction with misoprostol was more likely to be elective compared with the Foley catheter (70/265 [28.8%] vs 4/49 [12.1%]). A total of 238 multiparous women were induced with misoprostol and 65 with the Foley catheter. Again, multiparous women induced with misoprostol and the Foley catheter had similar baseline characteristics except for a higher median Bishop score among women induced with the Foley catheter.
| Characteristic | Nulliparous | Multiparous | ||||
|---|---|---|---|---|---|---|
| Misoprostol (n = 265) | Foley catheter (n = 49) | P value | Misoprostol (n = 238) | Foley catheter (n = 65) | P value | |
| Maternal age (y), mean (SD) | 22.4 (6.0) | 21.0 (5.0) | .12 | 27.3 (5.5) | 27.8 (5.8) | .50 |
| Maternal weight (kg), mean (SD) | 85.5 (18.7) | 82.4 (18.8) | .29 | 95.1 (22.5) | 88.8 (17.5) | .04 |
| Maternal BMI (kg/m 2 ), mean (SD) | 31.8 (6.6) | 31.4 (6.6) | .71 | 35.0 (8.0) | 33.5 (6.5) | .18 |
| Obese (BMI >30 kg/m 2 ), n (%) | 147 (57.0) | 25 (51.0) | .59 | 172 (73.2) | 40 (63.5) | .13 |
| Maternal race, n (%) | ||||||
| Black | 157 (60.4) | 37 (77.1) | .09 | 166 (70.3) | 48 (73.9) | .31 |
| White | 74 (28.5) | 8 (16.7) | 55 (23.3) | 16 (24.6) | ||
| Other | 29 (11.2) | 3 (6.3) | 15 (6.4) | 1 (1.5) | ||
| Chronic hypertension, n (%) | 10 (3.8) | 0 (0) | .37 | 20 (8.4) | 7 (10.8) | .55 |
| Diabetes, n (%) | 4 (1.5) | 2 (4.1) | .24 | 10 (4.2) | 4 (6.2) | .51 |
| Smoking, n (%) | 31 (11.7) | 9 (18.4) | .20 | 49 (20.6) | 18 (27.7) | .22 |
| Alcohol use, n (%) | 2 (0.8) | 0 (0) | > .99 | 2 (0.8) | 2 (3.1) | .20 |
| Indication for induction, n (%) | ||||||
| Elective | 70 (28.8) | 4 (12.1) | .02 | 81 (36.5) | 11 (29.0) | .47 |
| Oligohydramnios | 32 (13.2) | 5 (15.2) | 29 (13.1) | 6 (15.8) | ||
| Maternal comorbidity | 20 (8.2) | 3 (9.1) | 26 (11.7) | 8 (21.1) | ||
| Preeclampsia | 38 (15.6) | 4 (12.1) | 22 (9.9) | 2 (5.3) | ||
| Nonreassuring fetal status | 5 (2.1) | 5 (15.2) | 5 (2.3) | 1 (2.6) | ||
| PROM | 25 (10.3) | 3 (9.1) | 13 (5.9) | 4 (10.5) | ||
| Other | 53 (21.8) | 9 (27.3) | 46 (20.7) | 6 (15.8) | ||
| Admission Bishop score, median (range) | 2 (0–7) | 3 (1–8) | < .01 | 1 (0–7) | 3 (0–8) | < .01 |
| Admission cervical dilation, median (range) | 1 (0–2) | 1 (0–3) | < .01 | 1 (0–3) | 1 (0–3) | < .01 |
| Gestational age (wks), mean (SD) | 39.2 (1.4) | 39.1 (1.4) | .68 | 39.3 (1.3) | 39.4 (1.2) | .34 |
| Prior cesarean, n (%) | 0 | 0 | — | 0 | 24 (36.9) | < .01 |
| Fetal sex, n (%) | .09 | .85 | ||||
| Male | 121 (45.8) | 29 (59.2) | 114 (47.9) | 32 (49.2) | ||
| Female | 143 (54.2) | 20 (40.8) | 124 (52.1) | 33 (50.8) | ||
| Birthweight (g), mean (SD) | 3213 (551) | 3143 (632) | .42 | 3315 (567) | 3342 (399) | .72 |
| Macrosomia (birthweight >4000 g), n (%) | 12 (4.5) | 2 (4.1) | .99 | 18 (7.6) | 3 (4.6) | .58 |
| Oxytocin augmentation | 213 (80.4) | 44 (89.8) | .12 | 172 (72.3) | 55 (84.6) | .04 |
| Regional anesthesia, n (%) | 256 (96.6) | 47 (95.9) | .81 | 210 (88.2) | 60 (92.3) | .35 |
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
