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The active management of risk in multiparous pregnancy at term: association between a higher preventive labor induction rate and improved birth outcomes
To determine whether exposure of multiparous women to a high rate of preventive labor induction was associated with a significantly lower cesarean delivery rate.
Study Design
Retrospective cohort study involving 123 multiparous women, who were exposed to the frequent use of preventive labor induction, and 304 multiparous women, who received standard management. Rates of cesarean delivery and other adverse birth outcomes were compared in the 2 groups. Logistic regression controlled for confounding covariates.
Results
The exposed group had a lower cesarean delivery rate (adjusted odds ratio, 0.09; 0.8% vs 9.9%; P = .02) and a higher uncomplicated vaginal delivery rate (odds ratio, 0.53; 78.9% vs 66.4%; P = .01). Exposure was not associated with higher rates of other adverse birth outcomes.
Conclusion
Exposure of multiparous women to a high rate of preventive labor induction was significantly associated with improved birth outcomes, including a very low cesarean delivery rate. A prospective randomized trial is needed to determine causality.
Cesarean delivery, compared with simple vaginal delivery, is associated with higher rates of excessive blood loss, postpartum infection, and maternal mortality.
Study Group of the Canadian Perinatal Surveillance System Maternal mortality and severe morbidity associated with low-risk planned cesarean delivery versus planned vaginal delivery at term.
In 2006, the US national cesarean delivery rate reached an all time high of 31.1 %.
For Editors' Commentary, see Table of Contents
A recently described strategy for the reduction of group cesarean delivery rates involved the use of risk factors for cesarean delivery to guide the increased use of preventive labor induction.
A preventive approach to obstetric care in a rural hospital: association between higher rates of preventive induction of labor and lower rates of cesarean delivery.
Nicholson JM, Cronholm P, Kellar LC, Stenson M, Macones GA. Confirmation of the association between a high preventive labor induction rate and a low cesarean delivery rate. J Women's Health. In press.
This strategy is called the active management of risk in pregnancy at term (AMOR-IPAT). Within AMOR-IPAT, preventive labor induction is used to increase the likelihood that labor begins before conditions develop that make vaginal delivery less likely (eg, a fetus that has grown too large to pass through the maternal pelvis and/or a placenta that is no longer able to adequately support the fetus during labor).
Multiparous women without a history of cesarean delivery are especially well-suited for AMOR-IPAT. Multiparous women are more easily induced than nulliparous women,
and labor induction is safer in multiparous women than in multiparous women with a prior history of cesarean delivery (vaginal birth after cesarean [VBAC]).
In addition, problems encountered during previous deliveries, such as macrosomia and the need for assisted vaginal delivery, often provide useful information about the optimal timing of delivery in subsequent pregnancies. Finally, multiparous women make up the largest of the 3 obstetric groups
and so a significant change of cesarean use among multiparous women would have a proportionally larger impact on any population's overall cesarean delivery rate. Accordingly, we performed a study to determine whether there was a significant association between exposure of multiparous women to AMOR-IPAT and a lower cesarean delivery rate.
Materials and Methods
A retrospective cohort study-design was used to compare 123 sequentially delivered AMOR-IPAT-exposed multiparous women with 304 randomly selected nonexposed multiparous women. Of the exposed women, 60 were part of a previously published study involving women of mixed parity (study A)
Nicholson JM, Cronholm P, Kellar LC, Stenson M, Macones GA. Confirmation of the association between a high preventive labor induction rate and a low cesarean delivery rate. J Women's Health. In press.
Because no exposed multiparous women in these 2 studies experienced a cesarean delivery, additional sequentially delivered exposed multiparous women (4) were considered until an exposed multiparous woman was identified who had a cesarean delivery. Of the 304 randomly selected nonexposed women, 128 were part of study A. Study A randomly selected 3 nonexposed women for each exposed woman but did not match for parity group (nulliparous vs multiparous vs VBAC women).
In addition, 173 nonexposed women were part of study B. Study B randomly selected nonexposed women but matched exposed and nonexposed study subjects by maternal parity group.
Nicholson JM, Cronholm P, Kellar LC, Stenson M, Macones GA. Confirmation of the association between a high preventive labor induction rate and a low cesarean delivery rate. J Women's Health. In press.
No additional nonexposed women were added to the study related to the inclusion of the final 4 exposed women. All women in this study delivered between April 5, 1998, and Nov. 18, 2002, at an urban academic medical center. All study subjects had a singleton pregnancy, at least 1 prenatal care visit with a hospital maternity care provider, and were candidates for a trial of labor at 38 weeks' gestation (ie, no placenta previa, active HIV disease, or major fetal anomaly). All exposed women received their prenatal care and their labor management from family physicians. All nonexposed women received their prenatal care and their labor management from obstetricians. All cesarean deliveries were performed by obstetricians.
For women in the AMOR-IPAT exposed group, risk factors for cesarean delivery were identified and placed in 1 of 2 categories: (1) the uteroplacental insufficiency (UPI) category (ie, factors that accelerate placental aging), or (2) the cephalopelvic disproportion (CPD) category (ie, factors that accelerate fetal growth or limit pelvic diameter) (We prefer to use the term cephalopelvic disproportion [CPD] rather than failure to progress [FTP] because CPD better captures the underlying cause of preventable dystocia related to interactions that occur between maternal pelvic characteristics [diameter and soft tissue volume] and fetal morphology [weight, head circumference, and shoulder girth]). The published odds ratio for cesarean delivery for each risk factor
A preventive approach to obstetric care in a rural hospital: association between higher rates of preventive induction of labor and lower rates of cesarean delivery.
(Appendix 1). The total number of risk days that any given woman had in each risk category was then subtracted from 41 weeks 0 days of gestation to estimate a category-specific upper limit of the optimal time of delivery (UL-OTD). The lower of the 2 category-specific UL-OTDs for each woman was identified as her final estimated UL-OTD, but the final UL-OTD was never less than 38 weeks 0 days of gestation. If a woman had not had spontaneous labor by 1 week before her UL-OTD, then labor induction was scheduled to ensure that she delivered on or before her UL-OTD. Furthermore, if a woman was scheduled for labor induction and had an unfavorable uterine cervix (modified Bishop's score < 6),
then she was offered preinduction cervical ripening. For exposed women in this study, methods of preinduction cervical ripening included dinoprostone (prostaglandin E2), misoprostol (prostaglandin E1), and Foley bulb catheter with 60 mL of fluid. Occasionally, these methods of preinduction cervical ripening were combined.
For data analysis, the frequency and proportions of prenatal and intrapartum covariates present in the exposed and nonexposed groups were compared. Means and medians of continuous variables were calculated. Normal distributions were compared using the Student t test, and non-normal distributions were compared by using the Wilcoxon rank-sum test. Dichotomous and categorical variables were compared by using χ2 techniques (Fisher exact test). Relative risk was used as the measure of univariate association. Statistical significance for all tests was defined as a P ≤ .05, and a statistical trend was defined as a P value from > .05 to ≤ .30.
To compare the pre-38 weeks of gestation level of risk for cesarean delivery in the 2 groups, an indirect standardization procedure was performed.
For this analysis, the larger nonexposed group was used as the reference group. Prenatal risk factors that at least trended toward different levels (P ≤ .30) in the 2 study groups, and that at least trended toward an association with increased or decreased cesarean delivery rate in the nonexposed group, were used as variables in this comparison. A standardized cesarean ratio (SCR) was calculated by dividing the expected cesarean delivery rate in the exposed group by the actual cesarean delivery rate in the nonexposed group.
An intention to treat approach was taken in the analysis of all outcomes. The primary outcome of the study was mode of delivery. Four secondary outcomes were identified before the start of the study: (1) major perineal injury (third or fourth degree), (2) 1-minute APGAR score less than 4, (3) 5-minute APGAR scores less than 7, and (4) neonatal intensive care unit (NICU) admission. Univariate analyses that used χ2 methods were performed to evaluate the association between exposure to AMOR-IPAT and each of the 5 preidentified outcomes. Multiple logistic regression was used to adjust for potential confounding in the association between AMOR-IPAT exposure and each of the 5 preidentified outcomes. We also assessed the association between exposure to AMOR-IPAT and other birth outcomes using χ2 techniques.
To evaluate overall birth health, we used 2 composite outcomes. The adverse outcomes index (AOI) is a previously published score
that uses 10 specific weighted outcomes to “assess not only the occurrence of deliveries with poor outcomes but also the number and relative severity of the outcomes” in any given group (Appendix 2). The AOI was calculated for each individual in each group and the outcomes of the 2 groups were then compared by using Wilcoxon rank-sum analysis. In addition, we created a composite outcome called “uncomplicated vaginal delivery” that identified a vaginal delivery not associated with any of 4 other adverse outcomes: mechanical assistance (vacuum or forceps), major perineal injury (third- or fourth-degree tear), postpartum hemorrhage (> 500 mL), or NICU admission (Appendix 3). The rate of uncomplicated vaginal delivery was determined for each group, and the rates were compared by using χ2 techniques (Fisher exact test).
A comparison of the distributions of gestational age at delivery in the 2 groups was performed with the use of survival analysis techniques. We collapsed data related to gestational age at delivery, timing of induction, and mode of delivery into half-week substrata and then encoded the data so as to enable graphic representation. The length of first and second stages of labor, the length of maternal hospital stay, and the length of neonatal hospital stay for each mother-infant pair within each study group were determined. Thereafter, comparisons of these time intervals between study groups were performed by using Wilcoxon rank-sum testing. Data were analyzed using the STATA Statistical Program (version 8; College Station, TX). The institutional review board of the University of Pennsylvania approved this investigation.
Results
Table 1 identifies levels of risk factors by study exposure group. Thirteen of 24 variables were present at statistically different levels between the exposure groups, and another 4 variables were present at levels that trended toward statistical significance. Within this group of 17 variables, 5 were either significantly associated with cesarean delivery, or trended toward a significant association, in the nonexposed group. The 5 variables, with their respective relative risk for cesarean delivery, were as follows: advanced maternal age (relative risk [RR], 1.95; P = .10); African American race (RR, 2.24; P = .09); alcohol use (RR 3.6; P = .003); previous vacuum or forceps delivery (RR, 2.77; P = .04); and anemia in the first or second trimester (hemoglobin [hgb] ≤ 11 mg/dL) (RR, 1.88; P = .003). An indirect standardization procedure using these variables, and using the nonexposed group as the reference group, suggested that the AMOR-IPAT exposed group should have had a 10.6% cesarean delivery rate as compared with the 9.9% rate that occurred in the nonexposed group. The standardized cesarean delivery rate for the exposed group, as compared with the nonexposed group, was therefore 1.07. This indicates that the exposed group did not have a lower risk of cesarean delivery than the nonexposed group at the start of the term period of pregnancy.
Exposed women were characterized by 2 key findings: they presented to the hospital earlier in the term period than the nonexposed group, and they were more likely to deliver after induction of labor (61% vs 16.4%; RR, 3.71; 95% confidence interval [CI], 2.77-4.96) (Figure 1, A and B). In addition, exposed women had an earlier median gestational age of delivery (38.7 weeks vs 39.9 weeks; P < .001), and the pattern of the timing of delivery as a function of gestational age within the exposed group was regularly earlier than in the nonexposed group (Figure 2). The Cox proportional hazard ratio indicating earlier delivery in the exposed group was 2.19 (95% CI, 1.77-2.72; P < .001). The higher rate of labor induction in the exposed group was almost entirely because of the greater use of preventive induction (45.5% vs 3.3%; RR, 13.8; 95% CI, 7.30-26.2) (Table 3).
FIGURE 1Timing of delivery, mode of labor onset, and method of delivery of study groups as a function of gestational age
A, This shows in bar-graph form the distribution of timing of delivery by gestational age in the 2 study groups. B, This shows in bar-graph form the distribution of induction of labor by gestational age in the 2 study groups. C, This shows in bar-graph form the distribution of cesarean delivery by gestational age in the 2 study groups.
Nicholson. Active management of term, multiparous pregnancy risk. Am J Obstet Gynecol 2009.
If labor was induced, then the median gestational age in the exposed group at the time of birth was 16 days earlier (38.7 weeks vs 41.0 weeks; P < .001). If labor occurred spontaneously, then the median gestational age in the exposed group was 5 days earlier (39.3 weeks vs 40.0 weeks; P = .01). In addition, exposed women had a lower median modified cervical Bishop's score on admission (5 vs 8; P = .01), and they were more likely to receive prostaglandins medication (PGE2 or PGE1) for cervical ripening (28.5% vs 6.9%; RR, 4.12; 95% CI, 2.50- 6.78) (Table 2). Although the median time from admission to delivery was longer in the exposed group (11.6 hours vs 7.3 hours; P < .001), once labor started, the median length for both the first stage and the second stage was shorter in the exposed group as compared with the nonexposed group (258 minutes vs 280 minutes; P = .04; 14 minutes vs 17 minutes; P = .05, respectively). We did not censor women who had a cesarean delivery in our analysis of the duration of the various stages of labor. Hence, shorter first and second stages were noted in the exposed group even though 20 nonexposed women had a cesarean delivery before full cervical dilatation and 10 nonexposed women had a cesarean delivery as the end point of their second stage of labor.
TABLE 2Levels of intrapartum variables/factors by study group
Onset of labor in this study was defined by objective documentation of cervical change, so women in this study who presented at the hospital after cervical change had begun had a truncation of their actual duration of the first stage of labor;
Onset of labor in this study was defined by objective documentation of cervical change, so women in this study who presented at the hospital after cervical change had begun had a truncation of their actual duration of the first stage of labor;
CI, confidence interval; IUPC, intrauterine pressure catheter; MAP, mean atrial pressure; ROM, rupture of membranes.
Nicholson. Active management of term, multiparous pregnancy risk. Am J Obstet Gynecol 2009.
a Some inductions in the exposed group involved both types of prostaglandins;
b Augmented labor includes both slow labor and premature rupture of membranes without labor;
c Onset of labor in this study was defined by objective documentation of cervical change, so women in this study who presented at the hospital after cervical change had begun had a truncation of their actual duration of the first stage of labor;
The cesarean delivery rate in the exposed group was 0.8%, as compared with 9.9% in the nonexposed group (RR, 0.08; 95% CI, 0.01-0.60) (Table 3). AMOR-IPAT exposure was associated with a significantly lower rate of cesarean delivery rate for both UPI and CPD. The only cesarean delivery in the exposed group occurred because of excessive bleeding from a previously identified marginal placenta previa. Multiple logistic regression was used to adjust for covariates in the association between AMOR-IPAT exposure and cesarean delivery. Covariates in the final model included: AMOR-IPAT exposure (adjusted odds ratio [aOR], 0.09; 95% CI, 0.1-0.69), advanced maternal age (aOR, 2.97; 95% CI, 1.09-8.12), African American race (aOR, 3.53; 95% CI, 1.11-11.2), alcohol use (aOR, 4.43; 95% CI, 1.37-14.3), and epidural analgesia (aOR, 5.08; 95% CI, 1.41-18.29). The timing of cesarean delivery in each group, as a function of gestational age, is shown in Figure 1, C.
TABLE 3Induction of labor and cesarean delivery information: overall rates and indications
Percentages reflect proportion of all infant in each study group delivered by cesarean delivery as a function of mode of onset of labor; fractions represent proportion of infants delivered by cesarean delivery within each mode of labor onset group.
Percentages reflect proportion of all infant in each study group delivered by cesarean delivery as a function of mode of onset of labor; fractions represent proportion of infants delivered by cesarean delivery within each mode of labor onset group.
Percentages reflect proportion of all infant in each study group delivered by cesarean delivery as a function of mode of onset of labor; fractions represent proportion of infants delivered by cesarean delivery within each mode of labor onset group.
Percentages reflect proportion of all infant in each study group delivered by cesarean delivery as a function of mode of onset of labor; fractions represent proportion of infants delivered by cesarean delivery within each mode of labor onset group.
0.26
0.04-1.95
.14
NICU INFORMATION
NICU admission (overall)
7.3%
8.6%
0.86
0.41-1.77
.84
Sepsis—suspect or actual
2.4%
2.3%
1.35
0.51-3.56
.59
Respiratory—persistent TTN, pneumonia, or amniotic fluid/meconium aspiration
2.4%
2.3%
Hypoglycemia
0.8%
1.0%
Cardiac arrhythmia
0.8%
0.8%
GI problem
0%
0%
Significant congenital problem
0.8%
0.3%
Severe hyperbilirubinemia
0%
0.3%
COMPOSITE OUTCOMES
Adverse outcome index
4.1
4.7
—
—
.23
Uncomplicated vaginal birth
78.9%
66.4%
1.19
1.05-1.34
.01
CI, confidence interval; GI, gastrointestinal; IUGR, intrauterine growth rate; NICU, neonatal intensive care unit; TTN, transient tchypnea of the newborn.
Nicholson. Active management of term, multiparous pregnancy risk. Am J Obstet Gynecol 2009.
a When not specified, rates are based on entire study group;
b Percentages reflect proportion of all infant in each study group delivered by cesarean delivery as a function of mode of onset of labor; fractions represent proportion of infants delivered by cesarean delivery within each mode of labor onset group.
The mean AOI score was similar in the 2 groups (4.1 in the exposed group, compared with 4.7 in the nonexposed group; P = .23) (Appendix 2). However, the uncomplicated vaginal delivery rate was significantly higher in the exposed group (78.9% vs 66.4%; P = .01) (Appendix 3). As noted in Table 4, AMOR-IPAT exposure was associated with a lower rate of third- or fourth-degree perineal tear (0% vs 4.3%; P = .04). Because a case of major perineal trauma did not occur in the exposed group, adjustment for confounding could not be applied to this outcome. Women in the exposed group were also less likely to have either thick meconium at the time of amniotic membrane rupture (4.9% vs 13.8%; RR, 0.35; 95% CI, 0.15-0.81), or fetal macrosomia (birthweight > 8 lb, 7 oz) (5.7% vs 17.4%; RR, 0.33; 95% CI, 0.15-0.70).
TABLE 4Major other adverse outcomes based on AMOR-IPAT exposure status
Rates of NICU admission (6.5% vs 8.2%; P = .84) and low Apgar scoring at 1 and 5 minutes (6.5% vs 11.8%; P = .15; and 0.8% vs 1.0%; P = .87, respectively) were similar in the 2 groups, and multiple regression did not significantly alter the magnitude of these associations (data not shown). Rates of chorioamnionitis, assisted vaginal delivery, and cephalohematoma were similar in the 2 groups. The 2 study groups had similar rates of low birthweight infants (3.2% vs 2.3%; P = .57), but the exposed group had more infants who weighted less than 6 lb 8 oz (28.5% vs 13.8%; P < .001). However, of the 32 infants in the exposed group who weighed less than 2950 g at birth, only 3 required NICU admission, and of these, only 1 was delivered after induction of labor. This infant delivered at 38 weeks 5 days of gestation, the mother's labor was complicated by severe variable decelerations and a true knot in the umbilical cord, and the reason for NICU admission was possible sepsis rather than respiratory insufficiency.
Comment
This study finds a significant association in multiparas between exposure to a high rate of preventive labor induction (45.5% vs 3.3%; P < .001) through AMOR-IPAT and a very low cesarean delivery rate (0.8% vs 9.9%; P < .001). Rates of cesarean delivery in the exposed group were lower for both intolerance of labor and failure to progress. In addition, the group of women exposed to a higher rate of preventive labor induction had a significantly higher uncomplicated vaginal delivery rate (78.9% vs 66.4%; P = .01) and significantly lower rates of major perineal injury, excessive blood loss and passage of thick meconium. No important birth outcomes occurred with increased frequency in the exposed group.
The finding that a high rate of preventive labor induction that used AMOR-IPAT was associated with a lower cesarean delivery rate is consistent with the results of 2 recently published investigations. Specifically, a retrospective study from a rural secondary hospital
A preventive approach to obstetric care in a rural hospital: association between higher rates of preventive induction of labor and lower rates of cesarean delivery.
included 407 multiparous women exposed to a higher rate of preventive labor induction through AMOR-IPAT. The exposed group experienced a 1.2% cesarean delivery rate, whereas the nonexposed multiparous group experienced a 4.2% cesarean delivery rate (OR, 0.42; P = .008). Rates of other birth outcomes were not higher in the AMOR-IPAT exposed group. In addition, a 270 patient prospective trial from an urban setting
included 143 multiparous women. Seventy-one were exposed to a higher rate of labor induction through AMOR-IPAT and experienced a 2.9% cesarean delivery rate, whereas 72 received usual care and experienced a 5.6% cesarean delivery rate (OR, 0.51; P = .41). In the randomized trial, rates of other birth outcomes were not higher in the AMOR-IPAT exposed group. Although the randomized controlled trial failed to find statistical significance for the birth outcome “multiparous cesarean delivery,” the study was not powered to identify as statistically significant a 50% reduction of cesarean delivery in multiparous women. Taken collectively, both previous studies and the current study support the concept that AMOR-IPAT may be able to provide at least a 50% reduction in cesarean delivery risk in multiparous women.
In contrast to our findings, many previous studies of labor induction have linked labor induction in multiparous women to increased rates of both cesarean delivery and other adverse birth outcomes (herein after “adverse birth outcomes”).
Indicated labor induction with vaginal prostaglandin E2 increases the risk of cesarean section even in multiparous women with no previous cesarean section.
In retrospective investigations of multiparous induction that ensured adequate cervical ripening, higher rates of labor induction have not been associated with higher rates of cesarean delivery.
Furthermore, the greatest source of potential concern in previous retrospective studies of labor induction is the issue of confounding by indication. If a retrospective study finds higher rates of adverse birth outcomes in multiparous women following labor induction for standard indications,
are the adverse outcomes due to the induction procedure itself, or are they due to the reasons the induction procedure was initiated? We believe that the central research question should not be: “do multiparous women undergoing labor induction experience higher rates of cesarean delivery and other adverse outcomes than multiparous women who have spontaneous labor develop” but rather: “how do the birth outcomes of one group of women (a group that experiences a relatively high rate of preventive labor induction) compare with the birth outcomes of another group of women (a group that experiences a more standard rate of labor induction for standard indications).” Although the practice-based perspective is not commonly used in the retrospective study of the association between labor induction and cesarean delivery, we believe that it is an appropriate and valid approach.
Rates of primary cesarean delivery are always lower in multiparous women compared with nulliparous women.
This is largely due to a simple selection issue: multiparous women are women who have successfully delivered vaginally and have never required cesarean delivery, whereas nulliparous women are women who have not yet had a successful trial of labor. However, because multiparous women make up the largest of the 3 obstetric groups (eg, nulliparous women, multiparous women, and VBAC women), a reduction of primary cesarean delivery rates in the multiparous group would have a proportionally larger impact on population-based cesarean delivery rates. For example, in an idealized population containing 30% nulliparous women (with cesarean delivery rate of 24%), 55% multiparous women (with a cesarean delivery rate of 9%), and 15% VBAC women (with a cesarean delivery rate of 80%), an 8% point decrease in cesarean delivery rate in the multiparous group would have almost twice the impact on the overall population cesarean delivery rate as an 8% point reduction in the nulliparous group, and almost 4 times the impact of an 8% point reduction in the VBAC group. For this reason, we believe that there should be an increased emphasis on the study of methods of care that could lower cesarean delivery rates, and rates of other adverse birth outcomes, in multiparous women.
As noted in this study, a group with a higher rate of preventive labor induction would be expected to have an average gestational age at delivery that is lower than a group exposed to a lower labor induction rate. Several recent studies reported increasing rates of adverse birth outcomes, including cesarean delivery, as a function of increasing gestational age during the term period of pregnancy.
The impact of the interaction between increasing gestational age and obstetrical risk on birth outcomes: evidence of a varying optimal time of delivery.
and might explain the increasing likelihood of obstructed labor with increasing gestational age. In addition, multiparous women, compared with nulliparous women, are more likely to have a high body mass index (BMI) at conception, develop gestational diabetes, and measure large for dates.
These 3 factors would be expected to increase the weight of a fetus at any given gestational age in the late term period, thereby exacerbating the gestational age-related risk of CPD. In addition, progressive placental aging is also known to occur during the term period of pregnancy,
and might explain the increasing likelihood of fetal intolerance of labor with increasing gestational age. Multiparous women are also more likely to have chronic hypertension, advanced maternal age, and iron-deficiency anemia.
These 3 risk factors would be expected to decrease the quality of placental function at any given gestational age in the late term period, thereby exacerbating the gestational age-related risk of UPI. Hence, despite the link between multiparity and low cesarean delivery rate, the use of a more active management style, that is, one that uses preventive labor induction to promote delivery relatively early in the term period, might lower even further the already reduced risk of cesarean delivery in multiparous women.
Some investigators have attempted to model multiple risk factors to predict cesarean risk.
We believe that early models were only partially successful because they did not include gestational age as a covariate. More recently, gestational age has been used in modeling,
but the purpose of this modeling was to predict increased risk of cesarean delivery at later gestational ages and to support the use of elective cesarean delivery during the late term period. In contrast, AMOR-IPAT uses predicted risk to guide the use of labor induction early in the term period of pregnancy to avoid the most common indications for cesarean delivery. With reference to planned delivery early in the term period, some critics have questioned the relationship between AMOR-IPAT and iatrogenic neonatal pulmonary problems. Although 1 exposed infant had respiratory insufficiency develop after an indicated induction for decreased fetal movement and a nonreactive NST, we did not encounter any neonates in this study that required NICU admission for pulmonary problems after early term preventive labor induction. However, it is important to emphasize that careful pregnancy dating, and the use of documented informed consent, are essential components of AMOR-IPAT.
Our study has several potential limitations. First, it is possible that factors other than AMOR-IPAT exposure may have accounted for some or all of the difference in outcomes between the exposed and nonexposed groups. However, an indirect standardization indicated similar levels of pre-38-week risk for cesarean risk in the 2 study groups. Second, exposed women came from 3 different family medicine offices and the nonexposed women came from 6 different obstetrics offices. Possible differences in charting styles may have led to information bias, and different styles of labor management may have affected the primary outcomes. It is well-known that a variety of provider characteristics have a significant impact on group cesarean delivery rates. However, most of the variables used in the logistic regression model were well defined and easily captured, for example, standard demographic variables (age, insurance status, and marital status), laboratory values (hemoglobin, Group B strep status), and clinical variables (height, substance abuse, type of analgesia). There was no evidence to suggest that the criteria for cesarean delivery were differentially applied by the 2 specialties, and all cesarean deliveries were performed by the obstetrics group. Finally, the study took place in an urban setting, was performed at an academic institution, and involved primarily African-American women. Hence, the generalizability of this study to other setting is unclear. However, the results of this article are similar to those noted in the multiparous women of a large retrospective study (n = 1969) that involved rural white women from a nonacademic setting.
A preventive approach to obstetric care in a rural hospital: association between higher rates of preventive induction of labor and lower rates of cesarean delivery.
Despite these limitations, this study found a strong association between AMOR-IPAT and 2 related outcomes in multiparous women: a very low cesarean delivery rate and a higher uncomplicated vaginal delivery rate. Althoug the active intervention used in AMOR-IPAT, that is, labor induction, is generally associated with higher levels of adverse birth outcomes, the impact of the increased use of preventive labor induction, with attention to preinduction cervical ripening, and from a practice-based perspective rather than a mode-of-labor-onset perspective, has not been previously considered. The findings of this study describe a possible means to safely lower cesarean delivery utilization in multiparous women. An adequately powered randomized controlled study involving the impact of AMOR-IPAT on cesarean delivery in multiparous women is needed to further investigate these findings.
Appendix 1
Tabled
1AMOR-IPAT - UL-OTD Calculation Sheet – this figure describes how the timing of preventive labor induction was determined in the AMOR-IPAT exposed group
A. Uteroplacental factors:
Odds ratio
Time units
History of chronic hypertension
1.8
6 days
____________________
Gestational diabetes
1.8
6 days
____________________
Insulin dependent diabetes
2.4
10 days
____________________
Sickle cell trait
1.5
3 days
____________________
Elevated AFP
1.4
3 days
____________________
Cigarette use
1.3
2 days
____________________
Size < dates (≤ 3 cm)
1.6
4 days
____________________
Advanced age (≥ 35 years at delivery)
1.8
6 days
____________________
Anemia (first trimester ≤ 10.0)
1.6
4 days
____________________
TOTAL UPI time units
____________________
ULOTD-UPI = (41 weeks – total UPI time units) =
____________________
B. Cephalopelvic factors:
Odds ratio
Time units
Elevated BMI (≥ 30)
1.3
2 days
____________________
Short stature (≤ 62 in)
1.8
6 days
____________________
Excess weight gain (≥ 30 lb)
1.8
6 days
____________________
Size > dates (≥ 3 cm)
1.7
4 days
____________________
Gestational diabetes
1.8
6 days
____________________
Type 1 diabetes
2.4
10 days
____________________
History vacuum/forceps
2.2
9 days
____________________
Previous macrosomia (≥ 4000 g)
2.0
7 days
____________________
TOTAL CPD time units
____________________
ULOTD-CPD = (41 weeks – total CPD time units) =
____________________
FINAL ULOTD, lower of the 2 ULOTDs (ULOTD-UPI vs ULOTD-CPD), but the final ULOTD is always ≥ 38 weeks.
AFP, alpha-feto protein; AMOR-IPAT, active management of risk in pregnancy at term; BMI, body mass index; CPD, celphalopelvic disproportion; ULOTD, upper limit of the optimal time of delivery; UPI, uteroplacental insufficiency.
Nicholson. Active management of term, multiparous pregnancy risk. Am J Obstet Gynecol 2009.
A preventive approach to obstetric care in a rural hospital: association between higher rates of preventive induction of labor and lower rates of cesarean delivery.
Nicholson JM, Cronholm P, Kellar LC, Stenson M, Macones GA. Confirmation of the association between a high preventive labor induction rate and a low cesarean delivery rate. J Women's Health. In press.
Indicated labor induction with vaginal prostaglandin E2 increases the risk of cesarean section even in multiparous women with no previous cesarean section.
The impact of the interaction between increasing gestational age and obstetrical risk on birth outcomes: evidence of a varying optimal time of delivery.
Cite this article as: Nicholson JM, Caughey A, Stenson MH, et al. The active management of risk in multiparous pregnancy at term: association between a higher preventive labor induction rate and improved birth outcomes. Am J Obstet Gynecol 2009;200:250.e1-250.e13.
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