- Email: [email protected]
Risk of cesarean delivery after induction at term in nulliparous women with an unfavorable cervix
Risk of cesarean delivery after induction at term in nulliparous women with an unfavorable cervix David P. Johnson, MD,a Nancy R. Davis, MPH,b and Allen J. Brown, BA, BSb Portland, Ore OBJECTIVE: The purpose of this study was to evaluate the effect of induction on the route of delivery in nulliparous women laboring at term in a community hospital system. STUDY DESIGN: From April 1997 to October 1999, there were 7282 deliveries in nulliparous patients who met inclusion criteria. Cesarean delivery rates were calculated for patients in spontaneous labor and for patients who underwent induction. RESULTS: Among 4635 women (63.7%) in spontaneous labor, the cesarean delivery rate was 11.5% versus 23.7% among the 2647 (36.3%) patients who underwent induction. An important variable that affected the delivery route was the Bishop score at the initiation of the induction. The cesarean delivery rate was 31.5% among patients whose Bishop score was <5 at induction versus 18.1% for patients with a score ≥5 (P < .001). CONCLUSION: The induction of labor in nulliparous patients, especially those women with an unfavorable cervix as measured by Bishop score, is associated with a significantly increased risk of cesarean delivery. (Am J Obstet Gynecol 2003;188:1565-72.)
Key words: Cesarean delivery, induction, Bishop score
The overall cesarean delivery rate within the Portland Service Area of the Providence Health System in Oregon was found to be rising, which reflected the trend that was being seen in other parts of the country.1 In early 1995 the cesarean delivery reduction project was initiated; it had the dual goals of decreasing the rate of avoidable cesarean deliveries and reducing the significant variation between various practitioners. The methods used during this 5-year multidisciplinary effort included (1) the identification of barriers to the achievement of a lower cesarean delivery rate, (2) the development of three separate practice guidelines (one each for vaginal birth after cesarean delivery, inductions, and active management of labor), and (3) the implementation of a feedback reporting system to provide individual and aggregate statistics on the use of the guidelines. When the project began, Providence had three hospitals in the Portland Service Area, with approximately 70 clinicians who delivered a total of 3000 babies annually.
From Women’s Healthcare Associates, LLC,a and the Providence Health System.b Presented at the Sixty-Ninth Annual Meeting of the Pacific Coast Obstetrical and Gynecological Society, Oct 22-27, 2002, Rancho Mirage, Calif. Reprint requests: David P. Johnson, MD, 9555 SW Barnes Road, Suite 100, Portland, OR 97225. © 2003, Mosby, Inc. All rights reserved. 0002-9378/2003 $30.00 + 0 doi:10.1067/mob.2003.458
The overall cesarean delivery rate before the project was 19.4%, with a wide variation among providers. By the end of 1999, cesarean delivery rates were virtually unchanged at the three hospitals. At that time, there were 133 providers who delivered >5200 babies annually, with a cesarean delivery rate of 20.0% and continued wide variation in individual provider rates. The purpose of this study is to explore the effects of induction on the mode of delivery for nulliparous women at term during the study period. Material and methods Data were obtained for all women who were admitted for labor to the labor and delivery units of the three Providence hospitals in the Portland Service Area during the study period of the second quarter 1997 through the third quarter 1999. Nulliparous women with a singleton pregnancy at 37 to 43 weeks’ gestation were included in the study. Women who underwent scheduled cesarean delivery or with a breech presentation were excluded. Data for the study were collected by a trained perinatal data coordinator, who was a registered nurse working on the obstetrics unit at one of the hospitals. The nurse conducted chart abstraction using a special data collection form that was designed to collect the key data elements that were necessary for the study. For instance, the nurse collected data on whether patients were admitted in active labor, on the Bishop score at admission or at the time 1565
1566 Johnson, Davis, and Brown
June 2003 Am J Obstet Gynecol
Table I. Patient characteristic data that were available: spontaneous labor versus induction groups Spontaneous labor group
Characteristic Maternal age Age ≥35 y Gestational wk Gestational wk ≥41 Gestational wk ≥42 Bishop score Epidural‡ Birth weight Birth weight ≥4000 g Male
No.
Mean (SD)
3891 3891 4635 4635 4635 4107 3048 3318 3318 3433
26.4 (5.98) 9.3% 39.5 (1.15) 18.1% 2.2% 8.19 (2.40) 72.6% 3426.4 (433.22) 8.3% 51.1%
Induction group
No. 2174 2174 2647 2647 2647 2222 1867 2016 2016 2079
Mean (SD) 26.8 (5.78) 10.1% 39.8 (1.35) 34.6% 8.0% 5.30 (2.31) 84.9% 3507.4 (510.98) 15.2% 52.5%
Test value (degrees of freedom) 2.482 (4622.21)* 0.89† 9.452 (4822.52)* 250.87† 139.29† 46.862 (4702.12)* 99.59† 5.933 (3727.49)* 62.14† 0.99†
P value (2-tailed) .013 .345 <.001 <.001 <.001 <.001 <.001 <.001 <.001 .319
*t test for unequal variances. †χ2 test, degrees of freedom = 1. ‡April 1997 to December 1998.
of induction, and on the name of the physician or midwife who managed the patient’s labor during the delivery. Trained data-entry personnel entered data into the study database, which was a Microsoft Access (version 2.0; Microsoft Corporation, Redmond, Wash) application that had been designed specifically for this study. Those women who met the inclusion criteria were classified into either the laboring group or the induction group. Women with premature rupture of membranes at term were included in the spontaneous labor group. The induction group included all the women who were scheduled for the induction of labor, regardless of the indication for the induction, whether medical or elective. The Bishop score was to be obtained for all women who were admitted to the labor and delivery unit.2 The induction group was divided into those women with a favorable cervix (Bishop score ≥5) and those women with an unfavorable cervix (Bishop score <5). The attending physician or a certified nurse midwife made all decisions regarding the management of labor. Cervical ripening agents were used when indicated. Commonly used agents in our institution include prostaglandin gel, dinoprostone (Cervidil), misoprostol, and Foley balloon with extra-amniotic saline solution infusion. Intravenous oxytocin was used as the induction agent in both of the induction subgroups, unless labor ensued after cervical ripening or amniotomy. Epidural analgesia is used commonly in our units, with 72.6% of women in spontaneous labor and 84.9% of women being induced, having placement during the labor process. The decision for the timing and type of analgesia was again left up to the individual managing practitioner. Study data were linked electronically and merged with existing demographic data from the electronic claims databases of the hospitals. Data were then analyzed with the use of a variety of statistical software applications including Microsoft Excel 2000 (Microsoft Corporation), Epi Info 2000 (version 1.1; Centers for Disease Control
and Prevention, Atlanta, Ga), and SPSS for Windows (Release 11.0.1; SPSS Inc, Chicago, Ill). Statistical tests of significance included t-tests for equality of means with unequal variances for the demographic data (patient age, baby’s gestational age, Bishop score, and birth weight) and the χ2 test for the comparison of categoric data. Multiple logistic regression analysis was also performed to assess the relationship between several explanatory and confounding variables and the categoric response variable of cesarean delivery. Results There were 19,923 deliveries in the Portland Service Area of the Providence Health System during the study period, of whom 7282 were nulliparous women who had been admitted for spontaneous labor or induction of labor at term and who were included in the present study. The spontaneous labor group included 4635 women (63.7%); the induction group included 2647 women (36.3%). The Bishop score was not available for 528 women (11.4%) in the spontaneous labor group and 425 women(16.1%) in the induction group. Of the 4107 women in the spontaneous labor group with an available Bishop score, 3864 women (94.1%) were found to have a Bishop score of ≥5, and 243 women (5.9%) were found to have a Bishop score of <5. For the 2222 women who were included in the induction group with an available Bishop score, 1384 women (62.3%) were found to have a Bishop score of ≥5, and 838 women (37.7%) were found to have a Bishop score of <5. The patient characteristics differed significantly between the spontaneous labor and the induction groups (Table I). In some categories, the statistically significant differences were not clinically meaningful, primarily because of the large sample size of this study. For instance, the mean maternal age was 26.4 years for the spontaneous labor group and 26.8 years for the induction pa-
Johnson, Davis, and Brown 1567
Volume 188, Number 6 Am J Obstet Gynecol
Figure. Cesarean delivery rate in induced primiparous patients, by Bishop score.
tients (P < .05). Similarly, the gestational age was statistically significant (39.5 weeks in the spontaneous labor group and 39.8 weeks in the induction group, P < .001). For other variables, the differences were likely to be more clinically relevant. For instance, the Bishop score was significantly higher in the spontaneous labor group (8.19 vs 5.30 in induced patients, P < .001), and there were significantly more induced patients with a gestation of ≥41 weeks (34.6% vs 18.1% in spontaneous labor patients, P < .001). The cesarean delivery rate for women in spontaneous labor was 11.5%; women who were admitted for induction of labor were found to have a cesarean delivery rate of 23.7%. The cesarean delivery rate for women who were induced with an unfavorable cervix was 31.5%; the rate for women who were induced with a favorable cervix was 18.1% (Figure). The induction of labor for women with an unfavorable cervix was associated with a significantly increased risk of cesarean delivery (P < .001). Indications for the cesarean deliveries were not significantly different between the spontaneous labor group and the induction group. Failure to progress was the most common indication (51.0% in the spontaneous labor patients, and 54.5% in the induction patients), followed by fetal distress (29.1% in the spontaneous labor patients and 29.0% in the induction patients, Table II). Multiple logistic regression analysis was performed to assess the relationship between induced labor and a Bishop score of <5 with cesarean delivery, controlling for several confounding variables. The four confounders in the logistic regression model were (1) maternal age of ≥35 years, (2) male sex, (3) birth weight of ≥4000 g, and (4) baby’s gestational age in weeks. We also examined possible interactions between the exposure variables and the confounders. Among the cohort of 7282 women in this study, 3697 women (50.8%) had complete data for
Table II. Indications for cesarean delivery Indication Failure to progress Fetal distress Other No reason noted Total
Spontaneous labor group (No.)
Induction group (No.)
272 (51.0%) 155 (29.1%) 76 (14.3%) 30 (5.6%) 533 (100%)
342 (54.5%) 182 (29.0%) 78 (12.4%) 25 (4.0%) 627 (100%)
Differences between the spontaneous labor and induction groups were not statistically significant (χ2 test = 3.027, degrees of freedom = 3, P = .39).
the two exposure variables and four confounders; only this subset of women with complete data were used in the regression analysis. None of the interactions between the exposure and confounding variables were found to be significant, so interactions were dropped. The subsequent logistic regression analysis showed that all six of the variables had a significant relationship with cesarean delivery (Table III). The odds ratios for induction and a Bishop score of <5 were corrected to better estimate relative risk.3 Results show that after being controlled for confounders, there is a 77% greater risk for cesarean delivery after the induction of labor and a 76% greater risk for cesarean delivery for women with an unfavorable cervix (Table IV). Moreover, the inducement of labor in women with Bishop scores of <5 results in three times the risk for cesarean delivery than for women in spontaneous labor with Bishop scores of ≥5. Comment We found that the induction of labor at term of a nulliparous woman in our institution results in a significantly increased risk for delivery by cesarean delivery, especially
1568 Johnson, Davis, and Brown
June 2003 Am J Obstet Gynecol
Table III. Logistic regression of factors associated with cesarean delivery (n = 3697) Factor Induced Bishop score <5 Maternal age ≥35 y Birth weight ≥4000 g Gestational age (wk) Male Constant
β 0.66 0.68 0.95 0.76 0.23 0.30 –11.63
SE 0.11 0.12 0.15 0.13 0.04 0.10 1.66
Wald χ2
P value
Bivariate odds ratio (95% CI)*
Odds ratio (95% CI)
37.44 32.73 42.52 35.12 29.50 9.22 48.89
<.001 <.001 <.001 <.001 <.001 .002 <.001
2.73 (2.27-3.29) 2.88 (2.35-3.53) 2.41 (1.84-3.15) 2.91 (2.30-3.67) NA 1.39 (1.15-1.67) —
1.93 (1.56-2.38) 1.96 (1.56-2.47) 2.59 (1.94-3.44) 2.14 (1.67-2.76) 1.25 (1.16-1.36) 1.35 (1.11-1.64) —
NA, Not applicable. *Odds ratio between factor and cesarean delivery, without being controlled for other factors.
Table IV. Estimated relative risks for cesarean delivery as a factor of induction and Bishop score <5 Factor Spontaneous labor and Bishop score ≥5 Bishop score <5 Induced labor Induced labor and Bishop score <5
Estimated relative risk (95% CI)* Referent 1.76 (1.48-2.09) 1.77 (1.46-2.11) 3.00 (2.38-3.73)
*Based on adjusted odds ratios from logistic regression analysis.
when the cervix is unfavorable. The association between induction and increased risk for cesarean delivery has been documented in many studies,4,5 especially when the focusing is placed specifically on nulliparous patients.6,7 Studies that evaluated the induction of nulliparous patients consistently have shown an increased risk for cesarean delivery, although not always statistical significance has not always been reached. Most of these studies have found that there is a 2-fold increased risk for cesarean delivery with an induction of labor compared to spontaneous labor. Seyb et al6 prospectively studied 1561 nulliparous women at term in either spontaneous labor or awaiting induction. This included 437 women who labor was being induced both electively and for medical indications. The increased risk for cesarean delivery that was attributed to induction was found to be significant (7.8% for those in spontaneous labor vs 17.6% for the induction group). They included the results of the initial cervical examination by dilation and separately for effacement, but not together, to determine cervical favorability. They did note that the spontaneous labor group generally had more advanced dilation and effacement. They also did not determine the cesarean rates on the basis of the initial cervical assessment. It is interesting to note that, even with a much lower background cesarean rate at their institution, inductions were associated with a doubling of the cesarean delivery rate. The most significant finding of our study is one that is not necessarily very surprising. In the subgroup of those
women with an unfavorable cervix whose labor was induced, the cesarean delivery rate was the highest (31.5%), a result which is consistent with previous studies. Bishop2 demonstrated in 1964 that, using his scoring system, the status of the cervix is highly predictable of the probability for vaginal delivery. His study used multiparous women and defined a favorable cervix as being one with a score of ≥8. There are a multitude of studies that show a similar result.8-10 The American College of Obstetricians and Gynecologists practice bulletin “Induction of Labor” states, “Generally, induction of labor has merit as a therapeutic option when the benefits of expeditious delivery outweigh the risks of continuing the pregnancy. The benefits of labor induction must be weighed against the potential maternal or fetal risks associated with this procedure.”11 It then follows that, given the significantly elevated risk for delivery by cesarean delivery, the induction of labor in nulliparous patients should be approached with caution. This is particularly true if the cervix is unfavorable and the indication is either elective in nature or marginally medically indicated. It would also be appropriate to include this information on elevated risk of cesarean delivery as part of an informed consent discussion with a patient who is considering an elective induction. Patients may very well choose to delay or avoid inductions if they are fully aware of the weight of evidence regarding increased risk of cesarean delivery with inductions. It appears that important steps could be taken in our institution to reduce the need for cesarean delivery, including the prevention of the elective induction of nulliparous patients with an unfavorable cervix. The corollary to this would be to admit nulliparous patients to the labor unit only when they are in active labor and therefore, by definition, have a favorable cervix. Such actions would have both immediate and long-term implications for cesarean delivery rates, as the number of patients undergoing vaginal birth after cesarean has decreased. A recent policy has been adopted at our institution that discourages the use of cervical ripening agents in patients who are electively induced. Although this may have some effect, the real challenge is how to bring about
Volume 188, Number 6 Am J Obstet Gynecol
a cultural change in the way obstetrics is practiced in a particular hospital unit. This topic would be worthy of further study, both at our own institution and at others. We thank John D. Stull, MD, MPH, at the Department of Public Health and Preventive Medicine, Oregon Health and Sciences University, for his editorial and statistical review of this manuscript. REFERENCES
1. Clarke SC, Taffel SM. Rates of cesarean and VBAC delivery, United States, 1994. Birth 1996;23:166-8. 2. Bishop EH. Pelvic scoring for elective induction. Obstet Gynecol 1964;24:266-8. 3. Zhang J, Yu KF. What’s the relative risk? A method of correcting the odds ratio in cohort studies of common outcomes. JAMA 1998;280:1690-1. 4. Yeast JD, Jones A, Poskin M. Induction of labor and the relationship to cesarean delivery: a review of 7001 consecutive inductions. Am J Obstet Gynecol 1999;180:628-33. 5. Maslow AS, Sweeny AL. Elective induction of labor as a risk factor for cesarean delivery among low-risk women at term. Am J Obstet Gynecol 2000;95:917-22. 6. Seyb ST, Berka RJ, Socol ML, Dooley SL. Risk of cesarean delivery with elective induction of labor at term in nulliparous women. Obstet Gynecol 1999;94:600-7. 7. Ecker JL, Chen KT, Cohen AP, Riley LE, Lieberman ES. Increased risk of cesarean delivery with advancing maternal age: indications and associated factors in nulliparous women. Am J Obstet Gynecol 2001;185:883-7. 8. Burnett JE. Preinduction scoring: an objective approach to induction of labor. Obstet Gynecol 1966;28:479-83. 9. Friedman EA, Niswander KR, Bayonet-Rivera NP, Sachtleben MR. Prelabor status evaluation, II: weighted score. Obstet Gynecol 1967;29:539-44. 10. Dhall K, Grover V, Makendru SK. Prelabor status evaluation and course of labor. Asia Oceana J Obstet Gynaecol 1986;12:25-31. 11. American College of Obstetricians and Gynecologists. Induction of labor. Washington (DC): The College; 1999. ACOG technical bulletin No.: 10.
Editors’ note: This manuscript was revised after these discussions were presented. DR E. PAUL KIRK, Portland, Ore. This paper, an observation of obstetric practices in a major health system between April 1997 and October 1999, including three hospitals in the Portland Metropolitan area, is an important commentary on contemporary practice. The main conclusion, that the induction of labor in nulliparous patients, especially with those women with an unfavorable cervix as measured by a Bishop score, is associated with a significantly increased risk of cesarean delivery, is relevant and important and is in danger of being ignored. Now that we are in the early 21st century, we seem to have reached a new period in the fascinating history of cesarean delivery in obstetric practice. We have long moved through the periods of initial great controversy, the concerned caution of the first one half of the last century, the careful selection through the third quarter, and the concern about the rapidly increasing rates in the last quarter to our current state of acceptance of the cesarean delivery rate in the 21st century. Acceptance or complacency?
Johnson, Davis, and Brown 1569
The data are well known. The most recent vital statistics report1 that was published in February 2002 for the year 2000 reports a primary cesarean delivery rate of 16.1 per 100 live births, 10% more than the level reported for 1996 through 1997 and an overall rate of cesarean delivery of 22.9% of all births, which was an increase for the fourth consecutive year. This represents an 11% increase since 1996 and a rate that is now the highest to be reported since 1989 when the data first became available from birth certificates. In our region, the rates vary from a low of 14.5% in Hawaii to a high of 23.4% in California. In the last decade, the rate of the induction of labor has more than doubled from 9% in 1989 to 19.9% in 2000. In this study, it was 36.6%. We understand the reasons for this increase: the avoidance of difficult instrumental delivery and vaginal breech birth, revised management plans for patients with previous cesarean deliveries, the determination to eliminate intrapartum hypoxic injury, and respect for autonomy, patient choice, and the pelvic floor. However, the induction of labor is rarely on the list. We used to see our editorials headed “What is the right number of cesarean deliveries?”2 but now it is more likely to be “Should doctors perform elective cesarean delivery on request?”3 Many investigators have considered the search for the ideal section rate futile, because the ideal section rate is that which produces optimal outcomes. A recent paper concluded that the risk adjusted primary cesarean delivery rates are a marker for neonatal outcomes and observed that “units with a lower cesarean delivery rate than predicted had a higher incidence of asphyxia among the infants,” which implies that the low cesarean delivery rates had poorer outcomes, but that “units with a higher than predicted section rate” also had more babies with asphyxia.4 The authors concluded that, at hospitals at which the cesarean delivery rate was within the predicted range, more of the hypoxic infants underwent a cesarean delivery, which suggests that although they performed fewer cesarean deliveries overall, they more effectively chose with wisdom when to perform a cesarean delivery. Many recent studies have demonstrated the increased cesarean delivery rates after induction. From Kansas City in 1999, for nulliparous patients who had elective induction of labor, the risk of cesarean delivery was twice that of nulliparous patients who had spontaneous labor.5 From Brigham and Women’s in 1998, part of the high rate of cesarean delivery among older women who labor was explained by a higher rate of induction, particularly elective induction.6 From Tacoma, Wash, in 2000, elective induction significantly increased the risk of cesarean delivery for nulliparous women and increased the hospital predelivery time and costs.7 In 1999, from Northwestern in Chicago came a conclusion that “avoiding labor induction in settings of unproved benefit may aid efforts to reduce the primary cesarean delivery rate.”8 Although
1570 Johnson, Davis, and Brown
practice patterns are changing with an observed increase in the incidence of induction, investigators from Minnesota who observed temporal changes in rates and reasons for the medical induction of term labor between 1980 and 1996 not only found an increased use of induction from 12.9% in 1980 to 25.8% in 1995, but also found that indications changed with a 2-fold increase in induction for postdate gestation, a 23-fold increase in induction for macrosomia, and a 15-fold increase in elective induction.9 The average gestational delivery of postdate pregnancies declined from 41.9 weeks in 1980 to 41 weeks in 1995, and it is unclear on what this redefinition of postdate pregnancies is based. Where is the evidence to support these changes of definition and practice? The study of Johnson et al has the virtues of a simple observational study. The conclusion is straightforward, that the induction of labor in nulliparous patients, especially those women with an unfavorable cervix, increases the risk of cesarean delivery delivery. This finding confirms those of other investigators and raises a number of questions: 1. Would patients as readily accept a recommendation for induction if they appreciated the increased risk of cesarean delivery? In other words, how informed is their consent? 2. If the patient is well informed, does this acceptance of a high risk of cesarean delivery simply reflect a change of attitude in the community in which a high rate is accepted readily, if not welcomed? 3. The introduction describes a cesarean delivery reduction project that was initiated in 1995, which developed preceptor practice guidelines for induction. They report that the overall cesarean delivery rate was unchanged after the initiation of the project but do not comment on any influence on the induction rate, which was 36.6% during the study. A paper by Luthy et al, to be presented later this afternoon, concludes that the labor management physician adds a significant independent effect to the risk model for cesarean delivery. One suspects that attitudes for the use of induction also vary from physician to physician, which either directly or indirectly affects the cesarean delivery rate. I was taught and have taught two things about induction: (1) there are no indications for induction, only indications for delivery and (2) there are two types of induction, easy or difficult, and that when faced with a difficult induction, the indication for delivery has to be particularly strong. Johnson et al did not comment on the relative strength of the indications for induction nor do they use the term social induction, information that was probably not available from the database. Nevertheless, they conclude that the real crux is how to bring about a cultural change in the way obstetrics is practiced in the particular units and
June 2003 Am J Obstet Gynecol
comment that this “however, is another subject.” Another subject, perhaps, but these observations are a good place to start. Please comment on the following items: 1. The adequacy of informed consent in induction practice; 2. Whether the acceptance of the high risk of cesarean delivery after induction reflects a change in societal attitude toward childbirth; 3. Whether the cesarean delivery reduction project had any impact over time on the rate of induction; 4. Whether specific attention was paid to wide variances in physicians practice; and 5. The scale of the additional cost that was incurred by this common practice.
REFERENCES
1. Martin JA, Hamilton BC, Ventura SJ, Menacker F, Park MM. Births: final data for 2000. Natl Vital Stat Rep 2002;50:1-104. 2. What is the right number of cesarean sections? [editorial] Lancet 1997;349:815. 3. Peterson-Brown S. Should doctors perform elective cesarean section on request? Yes, as long as the woman is fully informed. BMJ 1998;317:462-3. 4. Bailit JL, Garrett JM, Miller WC, McMahon JM, Cefalo RC. Hospital primary cesarean delivery rates and the risk of poor neonatal outcomes. Am J Obstet Gynecol 2002;187:721-7. 5. Yeast JD, Jones A, Postkin M. Induction of labor and the relationship to cesarean delivery: a review of 7001 consecutive inductions. Am J Obstet Gynecol 1999;180:628-33. 6. Ecker JL, Chen KT, Cohen AP, Riley LE, Lieberman ES. Increased risk of cesarean delivery with advancing maternal age: Indications and associated factors in nuliparous women. Am J Obstet Gynecol 2001;185:883-7. 7. Maslow AS, Sweeney AL. Elective induction of labor as a risk factor for cesarean delivery among low-risk women at term. Obstet Gynecol 2000;95:917-22. 8. Seyb ST, Berka RJ, Socol ML, Dooley SL. Risk of cesarean delivery with elective induction of labor at term in nulliparous women. Obstet Gynecol 1999;94:600-7. 9. Yawn BP, Wollan P, McKeon K, Field CS. Temporal changes in rates and reasons for medical induction of term labor, 19801996. Am J Obstet Gynecol 2001;184:611-9.
DR JOHN ENBOM, Corvallis, Ore. When you indicated the patient selection process at the beginning of the study, you indicated that it was extracted by a qualified perinatal nurse. Was the Bishop score per se stated in some of the records or in all of the records by the primary physician as well, or was this extrapolated by the clinical impression of the extractor? In your experience in this study or in reviewing the literature, do you feel that there may be a more accurate method for using a predictor such as the Bishop score? My recollection is that the Bishop score is primarily an indicator for nulliparous patient cervixes and may not be as accurate an indicator also for primagravidas. DR DAVID LAGREW, Laguna Hills, Calif. Did you compare the cesarean delivery rates in elective and in nonelective inductions? Did you compare the length of the labors between inductions and spontaneous labor? Have you cared to share these data with your physicians and patients?
Volume 188, Number 6 Am J Obstet Gynecol
DR HOWARD BLANCHETTE, Danbury, Conn. Why did you include the patients who had premature rupture of the membranes not in labor in the labor group? What proportion of your cohort actually did not achieve induction, in other words, did not get beyond the active phase of labor? DR MARILYN LAUGHEAD, Scottsdale, Ariz. What were the various agents that were used for induction and was there a difference in effectiveness? What was the morbidity in the neonates, particularly when comparing elective inductions to the medically indicated? DR RUSSELL LAROS, JR, San Francisco, Calif. I can tell you personally, I am discouraged at watching the use of induction at our institution. We do a lot of inductions, and most of them are being done for postdatism and a number of them are being done because the mother needs to deliver in our tertiary institution. In neither of these situations do patients need to deliver that day or even in the next 48 hours. The problems I see are (1) the thought that, now that we have prostaglandins and Foley bulbs, we can successfully induce anybody, any time, and (2) the fact that no one talks to the patient about the significant risk that the induction may fail. The lack of this discussion has patients arriving with the expectation that they will deliver in the next 14 hours. What is missing is a discussion of a trial of induction with the patient understanding the possibility of going home when nothing happens and trying again another day. I cannot understand why a woman who is at 41 to 42 weeks of gestation age, has an amniotic fluid index of 22 after 12 hours of contractions, and has no abnormalities of the fetal heart rate cannot go home? Let us all think about this approach. DR BARRY SCHIFRIN, Glendale, Calif. My question involves not only the duration of labor but also the time in labor in terms of latent phase, in an effort to see not only the obstetric factors but also to help elucidate the socalled physician factor in the timing and the frequency of cesarean delivery. Did you actually evaluate the women in the active phase or the second stage of labor? My most unusual indication for elective induction was put on the chart as a mineral deficiency. It seems that the lady was promised an emerald if she would deliver on a certain date. In conjunction with Dr Laros, I would also add that there are logistic problems other than the expectation of cesarean delivery that you have to deal with. We have a log jam for induction at our hospital (I do not know how many other people have such a problem), and people are very disappointed when you tell them they cannot be induced. It has created quite a bit of hassle on labor and delivery, with the nurses in trying to schedule and keep traffic to a reasonable level. Have you not only isolated the individual factors contributing to the high rate of cesarean delivery but also, in fact, tried to add them together? It may be possible to define a patient who has so many of those risk factors (age, weight, unfavor-
Johnson, Davis, and Brown 1571
able cervix, a male fetus for example); maybe induction should not be attempted because the risk of cesarean delivery in that group is so high that to get the 1 in 20 or 1 in 5 or 2 in 5 or 3 in 5 of those delivered vaginally is not worth the effort. Does anybody have an idea of what the operative risk of cesarean delivery should be before we do offer a patient an elective cesarean delivery? DR E. J. QUILLIGAN, Long Beach, Calif. Could you tell me whether cervical ripening agents were used in any of the patients; if so, what effect did it have on success? DR JOHNSON (Closing). As far as the informed consent, I believe that most physicians are at least cognizant of how induction increases the risk of cesarean delivery. However, I am not sure how much of that is transmitted to the patient; therefore, I do not believe that most patients are truly receiving an informed consent about induction. Regarding acceptance by society of the high rate of cesarean delivery, there has definitely been a change. I know I have seen it in my practice, and we have seen it in practices at the hospital where I practice, a definite change in that way. Patients still want a vaginal birth but only if it is convenient and painless and does not ruin their pelvic floor. As far as the induction rate, no we did not really make an impact on it. The induction rates probably stayed fairly constant and maybe have risen some. We definitely have a logjam at our hospital in inductions; trying to get them scheduled is difficult sometimes, and that is a factor. In the whole cesarean delivery reduction project, which again was a different subject maybe, but I think the single most important aspect has gotten lost. It was a component of the active management of labor protocol; you only admit a patient when she is in labor. It is perhaps a fairly simple concept, but it is a concept that gets lost many times. It is kind of corollary to this whole thing about inducing labor, unless really indicated, only for a patient with a favorable cervix. Admit patients in labor when they are really in labor, but that is another subject. We addressed the wide variance in physician practice. Again, it may be somewhat of a different subject, but during the project, we focused primarily, like many projects, on the outliers, the ones with the highest cesarean delivery rates. We did studies in which we looked at different practices and the differences between the high cesarean rate providers and providers with a lower cesarean delivery rate. We saw some differences, but we focused only on those with the highest rate. I think that was a mistake. There is a theory by Everett Rogers on the Diffusion of Innovations1 in which you look at how ideas are adopted by groups. It looks at how things are transmitted and how you can adopt things within a group or a society. This concept is used extensively in the business world and particularly in the high technology field but has been used rarely in health care. Looking back, and in the middle of the project, we should have focused more on what Everett Rogers would call the “Early adopters,” whereas the “lag-
1572 Johnson, Davis, and Brown
gards,” as he would call the people that would have had the highest cesarean delivery rate, were not going to be responsive to any overtures by this process. They are only brought along, if ever, when everyone else has been brought along to acceptance. No question that there is an additional cost associated with induction, in terms of a long time in labor and delivery, increased use of epidural, more medications used, and, of course, the high risk of cesarean delivery. Dr Enbom asked about the Bishop score; we had a place in there where the Bishop score was supposed to be entered by the physician. However, if it was not entered, then it was extrapolated by the perinatal nurse. You are correct, as originally published by Bishop, it involved multiparous patients. There are other studies that look at the state of the cervix, and this is what we thought gave the most numeric, quantifiable way of looking at the state of the cervix in terms such as the effacement, dilatation, and softening, which are all very important components to whether a patient delivers vaginally or has a successful induction. Dr Lagrew, we did not separate out between elective and medical inductions and in the database that we have, we were not able to do that. Likewise, we do not have data on the length of labor that we could comment on. You also asked about the failed induction or prolonged latent phase. We do not have that available. I think that is a good point; back in the cesarean delivery project, we looked at what are the differences between those providers who had a high cesarean delivery rate and those providers who had a low cesarean delivery rate. One of the main differences was at what point in labor the cesarean sections were done. I did chart reviews on all these patients and found that the high cesarean delivery rate providers in general did their cesarean deliveries, not necessarily in patients who had undergone inductions but in laboring patients when they were still in the latent phase. Whereas for the lower rate providers, they did their cesarean deliveries when the patients were in the active phase of labor and had arrested descent or did not progress. There def-
June 2003 Am J Obstet Gynecol
initely was a difference, but in this particular study, we did not address that element. The induction agents and cervical ripening were left up to the individual practitioner. Misoprostol, cervidil, prostaglandin gel, a Foley balloon, all were used as cervical ripening agents; if the patient went into labor naturally after that, then nothing else was added. The commonly used agent for induction otherwise would be oxytocin, and we have a standard protocol for that. During the cesarean delivery reduction project, the morbidity rate was evaluated, and we saw no increase in neonatal morbidity rates. Although, again, we did not in this study perform a breakdown between the two in terms of elective versus medical induction but we did not see any increased neonatal morbidity. Dr Blanchette asked about premature rupture of the membranes. Why did we include that in the spontaneous labor group? We had to include them somewhere. Some of these patients did go into labor spontaneously on their own; some of the patients obviously did need to be induced. If anything, this bias is towards raising the spontaneous labor cesarean delivery rate rather than the other way around. Dr Schifrin, we talked about the latent phase and definite logjam. I think that is a good point about linking the different risks together. We looked at a logistic regression model that had these different independent risk factors associated with an increased risk of cesarean delivery. Trying to put those together and coming up with a risk model based on having a patient that has two, three, or four of these different risk factors could help you to determine the risk of a cesarean delivery for that particular patient. I would imagine that we would need a larger sample size. Dr Quilligan asked about cervical ripening agents, and I think I answered that. REFERENCE
1. Rogers EM. Diffusion of innovations. 4th ed. New York: Free Press; 1995.
Key words: Cesarean delivery, induction, Bishop score
The overall cesarean delivery rate within the Portland Service Area of the Providence Health System in Oregon was found to be rising, which reflected the trend that was being seen in other parts of the country.1 In early 1995 the cesarean delivery reduction project was initiated; it had the dual goals of decreasing the rate of avoidable cesarean deliveries and reducing the significant variation between various practitioners. The methods used during this 5-year multidisciplinary effort included (1) the identification of barriers to the achievement of a lower cesarean delivery rate, (2) the development of three separate practice guidelines (one each for vaginal birth after cesarean delivery, inductions, and active management of labor), and (3) the implementation of a feedback reporting system to provide individual and aggregate statistics on the use of the guidelines. When the project began, Providence had three hospitals in the Portland Service Area, with approximately 70 clinicians who delivered a total of 3000 babies annually.
From Women’s Healthcare Associates, LLC,a and the Providence Health System.b Presented at the Sixty-Ninth Annual Meeting of the Pacific Coast Obstetrical and Gynecological Society, Oct 22-27, 2002, Rancho Mirage, Calif. Reprint requests: David P. Johnson, MD, 9555 SW Barnes Road, Suite 100, Portland, OR 97225. © 2003, Mosby, Inc. All rights reserved. 0002-9378/2003 $30.00 + 0 doi:10.1067/mob.2003.458
The overall cesarean delivery rate before the project was 19.4%, with a wide variation among providers. By the end of 1999, cesarean delivery rates were virtually unchanged at the three hospitals. At that time, there were 133 providers who delivered >5200 babies annually, with a cesarean delivery rate of 20.0% and continued wide variation in individual provider rates. The purpose of this study is to explore the effects of induction on the mode of delivery for nulliparous women at term during the study period. Material and methods Data were obtained for all women who were admitted for labor to the labor and delivery units of the three Providence hospitals in the Portland Service Area during the study period of the second quarter 1997 through the third quarter 1999. Nulliparous women with a singleton pregnancy at 37 to 43 weeks’ gestation were included in the study. Women who underwent scheduled cesarean delivery or with a breech presentation were excluded. Data for the study were collected by a trained perinatal data coordinator, who was a registered nurse working on the obstetrics unit at one of the hospitals. The nurse conducted chart abstraction using a special data collection form that was designed to collect the key data elements that were necessary for the study. For instance, the nurse collected data on whether patients were admitted in active labor, on the Bishop score at admission or at the time 1565
1566 Johnson, Davis, and Brown
June 2003 Am J Obstet Gynecol
Table I. Patient characteristic data that were available: spontaneous labor versus induction groups Spontaneous labor group
Characteristic Maternal age Age ≥35 y Gestational wk Gestational wk ≥41 Gestational wk ≥42 Bishop score Epidural‡ Birth weight Birth weight ≥4000 g Male
No.
Mean (SD)
3891 3891 4635 4635 4635 4107 3048 3318 3318 3433
26.4 (5.98) 9.3% 39.5 (1.15) 18.1% 2.2% 8.19 (2.40) 72.6% 3426.4 (433.22) 8.3% 51.1%
Induction group
No. 2174 2174 2647 2647 2647 2222 1867 2016 2016 2079
Mean (SD) 26.8 (5.78) 10.1% 39.8 (1.35) 34.6% 8.0% 5.30 (2.31) 84.9% 3507.4 (510.98) 15.2% 52.5%
Test value (degrees of freedom) 2.482 (4622.21)* 0.89† 9.452 (4822.52)* 250.87† 139.29† 46.862 (4702.12)* 99.59† 5.933 (3727.49)* 62.14† 0.99†
P value (2-tailed) .013 .345 <.001 <.001 <.001 <.001 <.001 <.001 <.001 .319
*t test for unequal variances. †χ2 test, degrees of freedom = 1. ‡April 1997 to December 1998.
of induction, and on the name of the physician or midwife who managed the patient’s labor during the delivery. Trained data-entry personnel entered data into the study database, which was a Microsoft Access (version 2.0; Microsoft Corporation, Redmond, Wash) application that had been designed specifically for this study. Those women who met the inclusion criteria were classified into either the laboring group or the induction group. Women with premature rupture of membranes at term were included in the spontaneous labor group. The induction group included all the women who were scheduled for the induction of labor, regardless of the indication for the induction, whether medical or elective. The Bishop score was to be obtained for all women who were admitted to the labor and delivery unit.2 The induction group was divided into those women with a favorable cervix (Bishop score ≥5) and those women with an unfavorable cervix (Bishop score <5). The attending physician or a certified nurse midwife made all decisions regarding the management of labor. Cervical ripening agents were used when indicated. Commonly used agents in our institution include prostaglandin gel, dinoprostone (Cervidil), misoprostol, and Foley balloon with extra-amniotic saline solution infusion. Intravenous oxytocin was used as the induction agent in both of the induction subgroups, unless labor ensued after cervical ripening or amniotomy. Epidural analgesia is used commonly in our units, with 72.6% of women in spontaneous labor and 84.9% of women being induced, having placement during the labor process. The decision for the timing and type of analgesia was again left up to the individual managing practitioner. Study data were linked electronically and merged with existing demographic data from the electronic claims databases of the hospitals. Data were then analyzed with the use of a variety of statistical software applications including Microsoft Excel 2000 (Microsoft Corporation), Epi Info 2000 (version 1.1; Centers for Disease Control
and Prevention, Atlanta, Ga), and SPSS for Windows (Release 11.0.1; SPSS Inc, Chicago, Ill). Statistical tests of significance included t-tests for equality of means with unequal variances for the demographic data (patient age, baby’s gestational age, Bishop score, and birth weight) and the χ2 test for the comparison of categoric data. Multiple logistic regression analysis was also performed to assess the relationship between several explanatory and confounding variables and the categoric response variable of cesarean delivery. Results There were 19,923 deliveries in the Portland Service Area of the Providence Health System during the study period, of whom 7282 were nulliparous women who had been admitted for spontaneous labor or induction of labor at term and who were included in the present study. The spontaneous labor group included 4635 women (63.7%); the induction group included 2647 women (36.3%). The Bishop score was not available for 528 women (11.4%) in the spontaneous labor group and 425 women(16.1%) in the induction group. Of the 4107 women in the spontaneous labor group with an available Bishop score, 3864 women (94.1%) were found to have a Bishop score of ≥5, and 243 women (5.9%) were found to have a Bishop score of <5. For the 2222 women who were included in the induction group with an available Bishop score, 1384 women (62.3%) were found to have a Bishop score of ≥5, and 838 women (37.7%) were found to have a Bishop score of <5. The patient characteristics differed significantly between the spontaneous labor and the induction groups (Table I). In some categories, the statistically significant differences were not clinically meaningful, primarily because of the large sample size of this study. For instance, the mean maternal age was 26.4 years for the spontaneous labor group and 26.8 years for the induction pa-
Johnson, Davis, and Brown 1567
Volume 188, Number 6 Am J Obstet Gynecol
Figure. Cesarean delivery rate in induced primiparous patients, by Bishop score.
tients (P < .05). Similarly, the gestational age was statistically significant (39.5 weeks in the spontaneous labor group and 39.8 weeks in the induction group, P < .001). For other variables, the differences were likely to be more clinically relevant. For instance, the Bishop score was significantly higher in the spontaneous labor group (8.19 vs 5.30 in induced patients, P < .001), and there were significantly more induced patients with a gestation of ≥41 weeks (34.6% vs 18.1% in spontaneous labor patients, P < .001). The cesarean delivery rate for women in spontaneous labor was 11.5%; women who were admitted for induction of labor were found to have a cesarean delivery rate of 23.7%. The cesarean delivery rate for women who were induced with an unfavorable cervix was 31.5%; the rate for women who were induced with a favorable cervix was 18.1% (Figure). The induction of labor for women with an unfavorable cervix was associated with a significantly increased risk of cesarean delivery (P < .001). Indications for the cesarean deliveries were not significantly different between the spontaneous labor group and the induction group. Failure to progress was the most common indication (51.0% in the spontaneous labor patients, and 54.5% in the induction patients), followed by fetal distress (29.1% in the spontaneous labor patients and 29.0% in the induction patients, Table II). Multiple logistic regression analysis was performed to assess the relationship between induced labor and a Bishop score of <5 with cesarean delivery, controlling for several confounding variables. The four confounders in the logistic regression model were (1) maternal age of ≥35 years, (2) male sex, (3) birth weight of ≥4000 g, and (4) baby’s gestational age in weeks. We also examined possible interactions between the exposure variables and the confounders. Among the cohort of 7282 women in this study, 3697 women (50.8%) had complete data for
Table II. Indications for cesarean delivery Indication Failure to progress Fetal distress Other No reason noted Total
Spontaneous labor group (No.)
Induction group (No.)
272 (51.0%) 155 (29.1%) 76 (14.3%) 30 (5.6%) 533 (100%)
342 (54.5%) 182 (29.0%) 78 (12.4%) 25 (4.0%) 627 (100%)
Differences between the spontaneous labor and induction groups were not statistically significant (χ2 test = 3.027, degrees of freedom = 3, P = .39).
the two exposure variables and four confounders; only this subset of women with complete data were used in the regression analysis. None of the interactions between the exposure and confounding variables were found to be significant, so interactions were dropped. The subsequent logistic regression analysis showed that all six of the variables had a significant relationship with cesarean delivery (Table III). The odds ratios for induction and a Bishop score of <5 were corrected to better estimate relative risk.3 Results show that after being controlled for confounders, there is a 77% greater risk for cesarean delivery after the induction of labor and a 76% greater risk for cesarean delivery for women with an unfavorable cervix (Table IV). Moreover, the inducement of labor in women with Bishop scores of <5 results in three times the risk for cesarean delivery than for women in spontaneous labor with Bishop scores of ≥5. Comment We found that the induction of labor at term of a nulliparous woman in our institution results in a significantly increased risk for delivery by cesarean delivery, especially
1568 Johnson, Davis, and Brown
June 2003 Am J Obstet Gynecol
Table III. Logistic regression of factors associated with cesarean delivery (n = 3697) Factor Induced Bishop score <5 Maternal age ≥35 y Birth weight ≥4000 g Gestational age (wk) Male Constant
β 0.66 0.68 0.95 0.76 0.23 0.30 –11.63
SE 0.11 0.12 0.15 0.13 0.04 0.10 1.66
Wald χ2
P value
Bivariate odds ratio (95% CI)*
Odds ratio (95% CI)
37.44 32.73 42.52 35.12 29.50 9.22 48.89
<.001 <.001 <.001 <.001 <.001 .002 <.001
2.73 (2.27-3.29) 2.88 (2.35-3.53) 2.41 (1.84-3.15) 2.91 (2.30-3.67) NA 1.39 (1.15-1.67) —
1.93 (1.56-2.38) 1.96 (1.56-2.47) 2.59 (1.94-3.44) 2.14 (1.67-2.76) 1.25 (1.16-1.36) 1.35 (1.11-1.64) —
NA, Not applicable. *Odds ratio between factor and cesarean delivery, without being controlled for other factors.
Table IV. Estimated relative risks for cesarean delivery as a factor of induction and Bishop score <5 Factor Spontaneous labor and Bishop score ≥5 Bishop score <5 Induced labor Induced labor and Bishop score <5
Estimated relative risk (95% CI)* Referent 1.76 (1.48-2.09) 1.77 (1.46-2.11) 3.00 (2.38-3.73)
*Based on adjusted odds ratios from logistic regression analysis.
when the cervix is unfavorable. The association between induction and increased risk for cesarean delivery has been documented in many studies,4,5 especially when the focusing is placed specifically on nulliparous patients.6,7 Studies that evaluated the induction of nulliparous patients consistently have shown an increased risk for cesarean delivery, although not always statistical significance has not always been reached. Most of these studies have found that there is a 2-fold increased risk for cesarean delivery with an induction of labor compared to spontaneous labor. Seyb et al6 prospectively studied 1561 nulliparous women at term in either spontaneous labor or awaiting induction. This included 437 women who labor was being induced both electively and for medical indications. The increased risk for cesarean delivery that was attributed to induction was found to be significant (7.8% for those in spontaneous labor vs 17.6% for the induction group). They included the results of the initial cervical examination by dilation and separately for effacement, but not together, to determine cervical favorability. They did note that the spontaneous labor group generally had more advanced dilation and effacement. They also did not determine the cesarean rates on the basis of the initial cervical assessment. It is interesting to note that, even with a much lower background cesarean rate at their institution, inductions were associated with a doubling of the cesarean delivery rate. The most significant finding of our study is one that is not necessarily very surprising. In the subgroup of those
women with an unfavorable cervix whose labor was induced, the cesarean delivery rate was the highest (31.5%), a result which is consistent with previous studies. Bishop2 demonstrated in 1964 that, using his scoring system, the status of the cervix is highly predictable of the probability for vaginal delivery. His study used multiparous women and defined a favorable cervix as being one with a score of ≥8. There are a multitude of studies that show a similar result.8-10 The American College of Obstetricians and Gynecologists practice bulletin “Induction of Labor” states, “Generally, induction of labor has merit as a therapeutic option when the benefits of expeditious delivery outweigh the risks of continuing the pregnancy. The benefits of labor induction must be weighed against the potential maternal or fetal risks associated with this procedure.”11 It then follows that, given the significantly elevated risk for delivery by cesarean delivery, the induction of labor in nulliparous patients should be approached with caution. This is particularly true if the cervix is unfavorable and the indication is either elective in nature or marginally medically indicated. It would also be appropriate to include this information on elevated risk of cesarean delivery as part of an informed consent discussion with a patient who is considering an elective induction. Patients may very well choose to delay or avoid inductions if they are fully aware of the weight of evidence regarding increased risk of cesarean delivery with inductions. It appears that important steps could be taken in our institution to reduce the need for cesarean delivery, including the prevention of the elective induction of nulliparous patients with an unfavorable cervix. The corollary to this would be to admit nulliparous patients to the labor unit only when they are in active labor and therefore, by definition, have a favorable cervix. Such actions would have both immediate and long-term implications for cesarean delivery rates, as the number of patients undergoing vaginal birth after cesarean has decreased. A recent policy has been adopted at our institution that discourages the use of cervical ripening agents in patients who are electively induced. Although this may have some effect, the real challenge is how to bring about
Volume 188, Number 6 Am J Obstet Gynecol
a cultural change in the way obstetrics is practiced in a particular hospital unit. This topic would be worthy of further study, both at our own institution and at others. We thank John D. Stull, MD, MPH, at the Department of Public Health and Preventive Medicine, Oregon Health and Sciences University, for his editorial and statistical review of this manuscript. REFERENCES
1. Clarke SC, Taffel SM. Rates of cesarean and VBAC delivery, United States, 1994. Birth 1996;23:166-8. 2. Bishop EH. Pelvic scoring for elective induction. Obstet Gynecol 1964;24:266-8. 3. Zhang J, Yu KF. What’s the relative risk? A method of correcting the odds ratio in cohort studies of common outcomes. JAMA 1998;280:1690-1. 4. Yeast JD, Jones A, Poskin M. Induction of labor and the relationship to cesarean delivery: a review of 7001 consecutive inductions. Am J Obstet Gynecol 1999;180:628-33. 5. Maslow AS, Sweeny AL. Elective induction of labor as a risk factor for cesarean delivery among low-risk women at term. Am J Obstet Gynecol 2000;95:917-22. 6. Seyb ST, Berka RJ, Socol ML, Dooley SL. Risk of cesarean delivery with elective induction of labor at term in nulliparous women. Obstet Gynecol 1999;94:600-7. 7. Ecker JL, Chen KT, Cohen AP, Riley LE, Lieberman ES. Increased risk of cesarean delivery with advancing maternal age: indications and associated factors in nulliparous women. Am J Obstet Gynecol 2001;185:883-7. 8. Burnett JE. Preinduction scoring: an objective approach to induction of labor. Obstet Gynecol 1966;28:479-83. 9. Friedman EA, Niswander KR, Bayonet-Rivera NP, Sachtleben MR. Prelabor status evaluation, II: weighted score. Obstet Gynecol 1967;29:539-44. 10. Dhall K, Grover V, Makendru SK. Prelabor status evaluation and course of labor. Asia Oceana J Obstet Gynaecol 1986;12:25-31. 11. American College of Obstetricians and Gynecologists. Induction of labor. Washington (DC): The College; 1999. ACOG technical bulletin No.: 10.
Editors’ note: This manuscript was revised after these discussions were presented. DR E. PAUL KIRK, Portland, Ore. This paper, an observation of obstetric practices in a major health system between April 1997 and October 1999, including three hospitals in the Portland Metropolitan area, is an important commentary on contemporary practice. The main conclusion, that the induction of labor in nulliparous patients, especially with those women with an unfavorable cervix as measured by a Bishop score, is associated with a significantly increased risk of cesarean delivery, is relevant and important and is in danger of being ignored. Now that we are in the early 21st century, we seem to have reached a new period in the fascinating history of cesarean delivery in obstetric practice. We have long moved through the periods of initial great controversy, the concerned caution of the first one half of the last century, the careful selection through the third quarter, and the concern about the rapidly increasing rates in the last quarter to our current state of acceptance of the cesarean delivery rate in the 21st century. Acceptance or complacency?
Johnson, Davis, and Brown 1569
The data are well known. The most recent vital statistics report1 that was published in February 2002 for the year 2000 reports a primary cesarean delivery rate of 16.1 per 100 live births, 10% more than the level reported for 1996 through 1997 and an overall rate of cesarean delivery of 22.9% of all births, which was an increase for the fourth consecutive year. This represents an 11% increase since 1996 and a rate that is now the highest to be reported since 1989 when the data first became available from birth certificates. In our region, the rates vary from a low of 14.5% in Hawaii to a high of 23.4% in California. In the last decade, the rate of the induction of labor has more than doubled from 9% in 1989 to 19.9% in 2000. In this study, it was 36.6%. We understand the reasons for this increase: the avoidance of difficult instrumental delivery and vaginal breech birth, revised management plans for patients with previous cesarean deliveries, the determination to eliminate intrapartum hypoxic injury, and respect for autonomy, patient choice, and the pelvic floor. However, the induction of labor is rarely on the list. We used to see our editorials headed “What is the right number of cesarean deliveries?”2 but now it is more likely to be “Should doctors perform elective cesarean delivery on request?”3 Many investigators have considered the search for the ideal section rate futile, because the ideal section rate is that which produces optimal outcomes. A recent paper concluded that the risk adjusted primary cesarean delivery rates are a marker for neonatal outcomes and observed that “units with a lower cesarean delivery rate than predicted had a higher incidence of asphyxia among the infants,” which implies that the low cesarean delivery rates had poorer outcomes, but that “units with a higher than predicted section rate” also had more babies with asphyxia.4 The authors concluded that, at hospitals at which the cesarean delivery rate was within the predicted range, more of the hypoxic infants underwent a cesarean delivery, which suggests that although they performed fewer cesarean deliveries overall, they more effectively chose with wisdom when to perform a cesarean delivery. Many recent studies have demonstrated the increased cesarean delivery rates after induction. From Kansas City in 1999, for nulliparous patients who had elective induction of labor, the risk of cesarean delivery was twice that of nulliparous patients who had spontaneous labor.5 From Brigham and Women’s in 1998, part of the high rate of cesarean delivery among older women who labor was explained by a higher rate of induction, particularly elective induction.6 From Tacoma, Wash, in 2000, elective induction significantly increased the risk of cesarean delivery for nulliparous women and increased the hospital predelivery time and costs.7 In 1999, from Northwestern in Chicago came a conclusion that “avoiding labor induction in settings of unproved benefit may aid efforts to reduce the primary cesarean delivery rate.”8 Although
1570 Johnson, Davis, and Brown
practice patterns are changing with an observed increase in the incidence of induction, investigators from Minnesota who observed temporal changes in rates and reasons for the medical induction of term labor between 1980 and 1996 not only found an increased use of induction from 12.9% in 1980 to 25.8% in 1995, but also found that indications changed with a 2-fold increase in induction for postdate gestation, a 23-fold increase in induction for macrosomia, and a 15-fold increase in elective induction.9 The average gestational delivery of postdate pregnancies declined from 41.9 weeks in 1980 to 41 weeks in 1995, and it is unclear on what this redefinition of postdate pregnancies is based. Where is the evidence to support these changes of definition and practice? The study of Johnson et al has the virtues of a simple observational study. The conclusion is straightforward, that the induction of labor in nulliparous patients, especially those women with an unfavorable cervix, increases the risk of cesarean delivery delivery. This finding confirms those of other investigators and raises a number of questions: 1. Would patients as readily accept a recommendation for induction if they appreciated the increased risk of cesarean delivery? In other words, how informed is their consent? 2. If the patient is well informed, does this acceptance of a high risk of cesarean delivery simply reflect a change of attitude in the community in which a high rate is accepted readily, if not welcomed? 3. The introduction describes a cesarean delivery reduction project that was initiated in 1995, which developed preceptor practice guidelines for induction. They report that the overall cesarean delivery rate was unchanged after the initiation of the project but do not comment on any influence on the induction rate, which was 36.6% during the study. A paper by Luthy et al, to be presented later this afternoon, concludes that the labor management physician adds a significant independent effect to the risk model for cesarean delivery. One suspects that attitudes for the use of induction also vary from physician to physician, which either directly or indirectly affects the cesarean delivery rate. I was taught and have taught two things about induction: (1) there are no indications for induction, only indications for delivery and (2) there are two types of induction, easy or difficult, and that when faced with a difficult induction, the indication for delivery has to be particularly strong. Johnson et al did not comment on the relative strength of the indications for induction nor do they use the term social induction, information that was probably not available from the database. Nevertheless, they conclude that the real crux is how to bring about a cultural change in the way obstetrics is practiced in the particular units and
June 2003 Am J Obstet Gynecol
comment that this “however, is another subject.” Another subject, perhaps, but these observations are a good place to start. Please comment on the following items: 1. The adequacy of informed consent in induction practice; 2. Whether the acceptance of the high risk of cesarean delivery after induction reflects a change in societal attitude toward childbirth; 3. Whether the cesarean delivery reduction project had any impact over time on the rate of induction; 4. Whether specific attention was paid to wide variances in physicians practice; and 5. The scale of the additional cost that was incurred by this common practice.
REFERENCES
1. Martin JA, Hamilton BC, Ventura SJ, Menacker F, Park MM. Births: final data for 2000. Natl Vital Stat Rep 2002;50:1-104. 2. What is the right number of cesarean sections? [editorial] Lancet 1997;349:815. 3. Peterson-Brown S. Should doctors perform elective cesarean section on request? Yes, as long as the woman is fully informed. BMJ 1998;317:462-3. 4. Bailit JL, Garrett JM, Miller WC, McMahon JM, Cefalo RC. Hospital primary cesarean delivery rates and the risk of poor neonatal outcomes. Am J Obstet Gynecol 2002;187:721-7. 5. Yeast JD, Jones A, Postkin M. Induction of labor and the relationship to cesarean delivery: a review of 7001 consecutive inductions. Am J Obstet Gynecol 1999;180:628-33. 6. Ecker JL, Chen KT, Cohen AP, Riley LE, Lieberman ES. Increased risk of cesarean delivery with advancing maternal age: Indications and associated factors in nuliparous women. Am J Obstet Gynecol 2001;185:883-7. 7. Maslow AS, Sweeney AL. Elective induction of labor as a risk factor for cesarean delivery among low-risk women at term. Obstet Gynecol 2000;95:917-22. 8. Seyb ST, Berka RJ, Socol ML, Dooley SL. Risk of cesarean delivery with elective induction of labor at term in nulliparous women. Obstet Gynecol 1999;94:600-7. 9. Yawn BP, Wollan P, McKeon K, Field CS. Temporal changes in rates and reasons for medical induction of term labor, 19801996. Am J Obstet Gynecol 2001;184:611-9.
DR JOHN ENBOM, Corvallis, Ore. When you indicated the patient selection process at the beginning of the study, you indicated that it was extracted by a qualified perinatal nurse. Was the Bishop score per se stated in some of the records or in all of the records by the primary physician as well, or was this extrapolated by the clinical impression of the extractor? In your experience in this study or in reviewing the literature, do you feel that there may be a more accurate method for using a predictor such as the Bishop score? My recollection is that the Bishop score is primarily an indicator for nulliparous patient cervixes and may not be as accurate an indicator also for primagravidas. DR DAVID LAGREW, Laguna Hills, Calif. Did you compare the cesarean delivery rates in elective and in nonelective inductions? Did you compare the length of the labors between inductions and spontaneous labor? Have you cared to share these data with your physicians and patients?
Volume 188, Number 6 Am J Obstet Gynecol
DR HOWARD BLANCHETTE, Danbury, Conn. Why did you include the patients who had premature rupture of the membranes not in labor in the labor group? What proportion of your cohort actually did not achieve induction, in other words, did not get beyond the active phase of labor? DR MARILYN LAUGHEAD, Scottsdale, Ariz. What were the various agents that were used for induction and was there a difference in effectiveness? What was the morbidity in the neonates, particularly when comparing elective inductions to the medically indicated? DR RUSSELL LAROS, JR, San Francisco, Calif. I can tell you personally, I am discouraged at watching the use of induction at our institution. We do a lot of inductions, and most of them are being done for postdatism and a number of them are being done because the mother needs to deliver in our tertiary institution. In neither of these situations do patients need to deliver that day or even in the next 48 hours. The problems I see are (1) the thought that, now that we have prostaglandins and Foley bulbs, we can successfully induce anybody, any time, and (2) the fact that no one talks to the patient about the significant risk that the induction may fail. The lack of this discussion has patients arriving with the expectation that they will deliver in the next 14 hours. What is missing is a discussion of a trial of induction with the patient understanding the possibility of going home when nothing happens and trying again another day. I cannot understand why a woman who is at 41 to 42 weeks of gestation age, has an amniotic fluid index of 22 after 12 hours of contractions, and has no abnormalities of the fetal heart rate cannot go home? Let us all think about this approach. DR BARRY SCHIFRIN, Glendale, Calif. My question involves not only the duration of labor but also the time in labor in terms of latent phase, in an effort to see not only the obstetric factors but also to help elucidate the socalled physician factor in the timing and the frequency of cesarean delivery. Did you actually evaluate the women in the active phase or the second stage of labor? My most unusual indication for elective induction was put on the chart as a mineral deficiency. It seems that the lady was promised an emerald if she would deliver on a certain date. In conjunction with Dr Laros, I would also add that there are logistic problems other than the expectation of cesarean delivery that you have to deal with. We have a log jam for induction at our hospital (I do not know how many other people have such a problem), and people are very disappointed when you tell them they cannot be induced. It has created quite a bit of hassle on labor and delivery, with the nurses in trying to schedule and keep traffic to a reasonable level. Have you not only isolated the individual factors contributing to the high rate of cesarean delivery but also, in fact, tried to add them together? It may be possible to define a patient who has so many of those risk factors (age, weight, unfavor-
Johnson, Davis, and Brown 1571
able cervix, a male fetus for example); maybe induction should not be attempted because the risk of cesarean delivery in that group is so high that to get the 1 in 20 or 1 in 5 or 2 in 5 or 3 in 5 of those delivered vaginally is not worth the effort. Does anybody have an idea of what the operative risk of cesarean delivery should be before we do offer a patient an elective cesarean delivery? DR E. J. QUILLIGAN, Long Beach, Calif. Could you tell me whether cervical ripening agents were used in any of the patients; if so, what effect did it have on success? DR JOHNSON (Closing). As far as the informed consent, I believe that most physicians are at least cognizant of how induction increases the risk of cesarean delivery. However, I am not sure how much of that is transmitted to the patient; therefore, I do not believe that most patients are truly receiving an informed consent about induction. Regarding acceptance by society of the high rate of cesarean delivery, there has definitely been a change. I know I have seen it in my practice, and we have seen it in practices at the hospital where I practice, a definite change in that way. Patients still want a vaginal birth but only if it is convenient and painless and does not ruin their pelvic floor. As far as the induction rate, no we did not really make an impact on it. The induction rates probably stayed fairly constant and maybe have risen some. We definitely have a logjam at our hospital in inductions; trying to get them scheduled is difficult sometimes, and that is a factor. In the whole cesarean delivery reduction project, which again was a different subject maybe, but I think the single most important aspect has gotten lost. It was a component of the active management of labor protocol; you only admit a patient when she is in labor. It is perhaps a fairly simple concept, but it is a concept that gets lost many times. It is kind of corollary to this whole thing about inducing labor, unless really indicated, only for a patient with a favorable cervix. Admit patients in labor when they are really in labor, but that is another subject. We addressed the wide variance in physician practice. Again, it may be somewhat of a different subject, but during the project, we focused primarily, like many projects, on the outliers, the ones with the highest cesarean delivery rates. We did studies in which we looked at different practices and the differences between the high cesarean rate providers and providers with a lower cesarean delivery rate. We saw some differences, but we focused only on those with the highest rate. I think that was a mistake. There is a theory by Everett Rogers on the Diffusion of Innovations1 in which you look at how ideas are adopted by groups. It looks at how things are transmitted and how you can adopt things within a group or a society. This concept is used extensively in the business world and particularly in the high technology field but has been used rarely in health care. Looking back, and in the middle of the project, we should have focused more on what Everett Rogers would call the “Early adopters,” whereas the “lag-
1572 Johnson, Davis, and Brown
gards,” as he would call the people that would have had the highest cesarean delivery rate, were not going to be responsive to any overtures by this process. They are only brought along, if ever, when everyone else has been brought along to acceptance. No question that there is an additional cost associated with induction, in terms of a long time in labor and delivery, increased use of epidural, more medications used, and, of course, the high risk of cesarean delivery. Dr Enbom asked about the Bishop score; we had a place in there where the Bishop score was supposed to be entered by the physician. However, if it was not entered, then it was extrapolated by the perinatal nurse. You are correct, as originally published by Bishop, it involved multiparous patients. There are other studies that look at the state of the cervix, and this is what we thought gave the most numeric, quantifiable way of looking at the state of the cervix in terms such as the effacement, dilatation, and softening, which are all very important components to whether a patient delivers vaginally or has a successful induction. Dr Lagrew, we did not separate out between elective and medical inductions and in the database that we have, we were not able to do that. Likewise, we do not have data on the length of labor that we could comment on. You also asked about the failed induction or prolonged latent phase. We do not have that available. I think that is a good point; back in the cesarean delivery project, we looked at what are the differences between those providers who had a high cesarean delivery rate and those providers who had a low cesarean delivery rate. One of the main differences was at what point in labor the cesarean sections were done. I did chart reviews on all these patients and found that the high cesarean delivery rate providers in general did their cesarean deliveries, not necessarily in patients who had undergone inductions but in laboring patients when they were still in the latent phase. Whereas for the lower rate providers, they did their cesarean deliveries when the patients were in the active phase of labor and had arrested descent or did not progress. There def-
June 2003 Am J Obstet Gynecol
initely was a difference, but in this particular study, we did not address that element. The induction agents and cervical ripening were left up to the individual practitioner. Misoprostol, cervidil, prostaglandin gel, a Foley balloon, all were used as cervical ripening agents; if the patient went into labor naturally after that, then nothing else was added. The commonly used agent for induction otherwise would be oxytocin, and we have a standard protocol for that. During the cesarean delivery reduction project, the morbidity rate was evaluated, and we saw no increase in neonatal morbidity rates. Although, again, we did not in this study perform a breakdown between the two in terms of elective versus medical induction but we did not see any increased neonatal morbidity. Dr Blanchette asked about premature rupture of the membranes. Why did we include that in the spontaneous labor group? We had to include them somewhere. Some of these patients did go into labor spontaneously on their own; some of the patients obviously did need to be induced. If anything, this bias is towards raising the spontaneous labor cesarean delivery rate rather than the other way around. Dr Schifrin, we talked about the latent phase and definite logjam. I think that is a good point about linking the different risks together. We looked at a logistic regression model that had these different independent risk factors associated with an increased risk of cesarean delivery. Trying to put those together and coming up with a risk model based on having a patient that has two, three, or four of these different risk factors could help you to determine the risk of a cesarean delivery for that particular patient. I would imagine that we would need a larger sample size. Dr Quilligan asked about cervical ripening agents, and I think I answered that. REFERENCE
1. Rogers EM. Diffusion of innovations. 4th ed. New York: Free Press; 1995.