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Obstetrics & Gynecology:
doi: 10.1097/AOG.0b013e318204521a
Original Research

The Singleton, Cephalic, Nulliparous Woman After 36 Weeks of Gestation: Contribution to Overall Cesarean Delivery Rates

Brennan, Donal J. MB, PhD; Murphy, Martina RGN; Robson, Michael S. MRCOG; O'Herlihy, Colm MD

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From the National Maternity Hospital, Dublin, Ireland; and the University College Dublin School of Medicine and Medical Science, National Maternity Hospital, Dublin, Ireland.

Presented at the Society for Maternal-Fetal Medicine 30th Annual Scientific Meeting, February 1–6, 2010, Chicago, Illinois.

Corresponding author: Michael Robson, National Maternity Hospital, Dublin 2, Ireland; e-mail: mrobson@nmh.ie.

Financial Disclosure The authors did not report any potential conflicts of interest.

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Abstract

OBJECTIVE: To examine the contribution of singleton, cephalic, term (37 weeks or later) nulliparous cesarean rates to overall cesarean incidence in a single institution during a 35-year period.

METHODS: Cesarean rates were examined for 1974, 1984, 1994, 1999, 2005, and 2008, applying a 10-group classification system. Groups 1 (spontaneously laboring, term nulliparous women) and 2 (prelabor cesarean and induced term nulliparous women) were combined as a composite variable—the term, singleton, cephalic nulliparous woman.

RESULTS: Overall and term, singleton, cephalic nulliparous cesarean rates correlated throughout the 35-year period (r=0.93, P<.001). Between 1974 and 2008, overall cesarean rates increased from 5% to 19.1% and from 4.4% to 15.8% among term, singleton, cephalic nulliparous women. Term, singleton, cephalic nulliparous inductions increased from 19.7% to 32.7% (P<.001) and the intrapartum cesarean rate in term, singleton, cephalic nulliparous inductions rose from 4.1% to 27.3%. The cesarean rate in group 1 increased from 2.3% to 7.2%.

CONCLUSION: The increase in term, singleton, cephalic nulliparous cesarean rates correlated with the increase in overall cesarean rates throughout 35 years in an institution with standard management of labor. This relationship was due to an increase in both the incidence and rate of cesarean delivery within term, singleton, cephalic nulliparous inductions. Examination of the different term, singleton, cephalic nullipara components (spontaneous labor, induction, or prelabor cesarean) can help to identify major variations in practice between institutions.

LEVEL OF EVIDENCE: III

Cesarean delivery rates have increased over the past four decades whereby it is now the most commonly performed surgical procedure in the developed world. This increase has been described by some healthcare providers as a public health issue of epidemic proportion.1,2 The World Health Organization has stated that a cesarean delivery rate greater than 10–15% is not justified,2 although rates in many developed countries now greatly exceed this suggested norm.

Several investigators have attempted to document the reasons underlying rising cesarean delivery rates3 and also to develop strategies that could potentially quantify or reduce these rates.4 Achievement of such goals requires a reliable and reproducible framework for audit and analysis of cesarean trends in specific obstetric subgroups, to permit comparisons of practice between different institutions and over time in the same institution. To this end, an all-inclusive 10-group classification system, described below, was devised in 2001.5 This objective system is prospectively determined, clinically relevant, self-validating, and robust and permits specific cesarean indications to be studied within individual groups.

Published data describing the 10-group classification have hitherto focused on studies in single institutions,6 or in national7 and international8,9 regions. Ten-group analysis has not been used, however, to examine local longitudinal cesarean delivery trends in a single obstetric center. The aim of the current study was to apply 10-group analysis to examine trends in obstetric outcomes in specific women delivered in an institution where a uniform approach to management of nulliparous labor has been used over 4 decades.

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MATERIALS AND METHODS

The National Maternity Hospital is a tertiary referral university institution that publishes an Annual Clinical Report, which includes detailed analysis of obstetric outcomes and modes of delivery of all delivered mothers and on all perinatal deaths (stillbirths and first-week neonatal deaths of infants who weighed more than 500 g, corrected for the exclusion of lethal malformations). Management of nulliparous labor has been standardized in the institution over the past four decades according to the Active Management of Labor protocol,10 the principles of which include accurate early diagnosis of labor and early correction of inefficient uterine action, continuously supported by a personal nurse throughout labor.11 The principles of active management of labor also emphasize the importance of auditing delivery outcomes in nulliparous women, and in multiparous women with and without cesarean delivery, spontaneous and induced labor, prelabor cesarean delivery, and single cephalic and other presentations. Data for 1974 and 1984 were collated from prospectively collected manual labor ward registers, and for all other subsequent years from a prospectively maintained computerized database. Data were discussed at a weekly audit conference and included in an annual clinical report that was prepared within 6 months of completion of the relevant calendar year. We reviewed the annual hospital reports and delivery registers for the years 1974, 1984, 1994, 1999, 2005, and 2008 and applied the 10-group classification. Institutional ethical approval was not required for this study.

The 10-group classification system is based on five intrinsic characteristics of every pregnancy, namely single or multiple; nulliparity or multiparity or multiparity with cesarean scar; cephalic or breech presentation or transverse lie; spontaneous or induced labor onset or prelabor cesarean delivery; and 37 or more weeks of gestation or preterm gestation.5 Definitions used for this study included: nulliparous: para 0, irrespective of gravidity; singleton gestation: no evidence of a multiple gestation after the first trimester; and term: 37 or more weeks of gestation. Induction of labor was defined as the use of any medication or amniotomy to initiate labor, rather than accelerate labor, that had already commenced spontaneously.

Data were analyzed using the 10-group classification system with reference to overall cesarean delivery rate, the size of each group, cesarean delivery rate in each individual group, and the contribution of each group to the total cesarean delivery rate. Groups 1 (spontaneously laboring term nulliparous women) and 2 (prelabor cesarean delivery and induced term nulliparous women) were combined as a composite variable—the term, singleton, cephalic nulliparous woman. Pearson's correlation coefficient was used to estimate the relationship between overall cesarean rates; term, singleton, cephalic nulliparous cesarean rates; and the group 1:2 ratio. Statistical analysis was calculated with the Mantel-Haenszel χ2 test with 1 degree of freedom.12 All calculations were performed using SPSS 11.0. P<.05 was considered statistically significant.

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RESULTS

During the 35 years from 1974 to 2008, a total of 264,750 mothers (annual average 7,564), including multiple pregnancies, were delivered after fetal viability (more than 500 g) of whom 109,147 (41.2%) women were nulliparous. The institutional cesarean delivery rate rose from 5% in 1974 to 19% in 2008 (3.8-fold) and the nonanomalous perinatal mortality rate fell from 14.6 per 1,000 in 1974 to 4.2 per 1,000 in 2008 (Table 1).

Table 1
Table 1
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Examination of the contribution of the 10 groups to the overall hospital population (Table 2) revealed that group 1 (spontaneously laboring term nulliparous women) remained relatively static over the time period studied, at 27%. During the 35-year period, significant increases were observed in groups 2a (induced term nulliparous women), 2b (prelabor term nulliparous women), 5 (previous and repeated cesarean delivery), 6 (nulliparous breech) and 8 (multiple pregnancies). The only significant decrease in contribution to the overall hospital population was in group 3 (spontaneously laboring term multiparous women). Closer examination of the changes in the hospital population during the 35-year period revealed a 3.4-fold increase in group 5 (previous and repeated cesarean delivery) from 2.6% in 1974 to 8.9% in 2008 (P<.001), consistent with the aforementioned rise in the institutional overall cesarean delivery rate. The second greatest increase (2.0-fold) was in group 2a (induced term nulliparous women), which rose from 6.7% of the overall hospital population in 1974 to 13.7% in 2008 (P<.001).

Table 2
Table 2
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We previously described a composite variable–the term, singleton, cephalic nulliparous woman— which combines groups 1 (spontaneously laboring term nulliparous women) and 2 (prelabor cesarean delivery and induced term nulliparous women).8 The contribution of the term, singleton, cephalic nulliparous woman to the overall hospital population was examined for the years 1974, 1984, 1994, 1999, 2005, and 2008. As illustrated in Figure 1, there was a progressive increase in term, singleton, cephalic nulliparous contribution to the overall obstetric population over the time period from 33.5% in 1974 to 42% (P<.001) in 2008.

Fig. 1
Fig. 1
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As already mentioned, there was a 3.8-fold increase in the overall institutional cesarean delivery rate between 1974 and 2008. Ten-group analysis was thus used to identify the major contributing factors to this phenomenon. Analysis of cesarean delivery rates within individual groups demonstrated a significant increase in all groups, except groups 2b (term nulliparous prelabor cesarean delivery), 4b (term multiparous prelabor cesarean delivery), and 9 (unstable lie), which should always be 100% (Table 3). The group 7 (multiparous breech) 12.3-fold increase, group 2a (induced term nulliparous women) 6.6-fold increase, and group 8 (multiple pregnancies) 5.7-fold increase represented the largest increases in cesarean delivery rates (Table 3). The group 1 (spontaneously laboring term nulliparous women) cesarean rate increased from 2.3% in 1974 to 7.2% in 2008 (3.13-fold increase, P=.03).

Table 3
Table 3
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As illustrated in Figure 2, there was an exponential increase in the term, singleton, cephalic nulliparous cesarean delivery rate from 4.4% in 1974 to 15.8% in 2008 (3.6-fold increase, P<.001). Institutional cesarean delivery rates correlated with term, singleton, cephalic nulliparous cesarean delivery rates throughout the 35-year period (r=0.93, r2=0.97, P=.007; Fig. 2). The r2 value of 0.97 suggests that 97% of the variation in overall institutional cesarean delivery rates over the 35 years could be explained by the rate among term, singleton, cephalic nulliparous women. Table 4 illustrates that the major contributor to the increased term, singleton, cephalic nulliparous cesarean delivery rate was an increased rate in term nulliparous inductions. Of note, term, singleton, cephalic nulliparous inductions increased from 19.7% (508/2,575) to 32.7% (1,233/3,776) (P<.001) and the intrapartum cesarean delivery rate in term, singleton, cephalic nulliparous inductions rose from 4.1% to 27.3% during the study period.

Fig. 2
Fig. 2
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Table 4
Table 4
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The contribution of different groups to the institutional cesarean delivery rate during the time period is illustrated in Figure 3. This demonstrates that group 2 (prelabor cesarean delivery and induced term nulliparous women) and group 5 (previous and repeated cesarean delivery) are the two major contributors to the institutional cesarean delivery rate. Closer evaluation demonstrates a 13.4-fold increase in the contribution of group 2 (prelabor cesarean delivery and induced term nulliparous women) and a 12.2-fold increase in the contribution of group 5 (previous and repeated cesarean delivery) to the institutional rate (Table 5). The influence of breech deliveries (groups 6 and 7), multiple pregnancies (group 8), or premature deliveries (group 10) on the institutional cesarean delivery rate did not vary significantly during the time period studied and does not contribute significantly to the overall cesarean delivery rate in absolute terms (Table 5).

Fig. 3
Fig. 3
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Table 5
Table 5
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The ratio of spontaneous laboring cephalic term nulliparous women to induced cephalic term nulliparous women and prelabor cesarean deliveries—that is, the ratio of the contribution of groups 1 and 2 to the overall hospital population (group 1:2 ratio)—has been proposed as a surrogate marker of institutional cesarean delivery rates.8 Examination of the group 1:2 ratio in our institution during the 35-year period revealed that it fell from 3.63 in 1974 to 1.87 in 2008 (Fig. 4). An inverse correlation was seen between the group 1:2 ratio and the institutional cesarean delivery rate (r=−0.84, r2=0.69, P=.041; Fig. 3); this r2 suggests that up to 69% of the variation in the institutional cesarean delivery rate throughout the time period studied can be attributed to nulliparous induction.

Fig. 4
Fig. 4
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DISCUSSION

This study offers an insight into changing obstetric populations and outcomes in a setting in which spontaneous nulliparous labor was managed in a standardized fashion throughout the 35 years studied. The results highlight term, singleton, cephalic nulliparous women as an important obstetric cohort and confirms the contribution of these cesarean delivery rates to an increasing institutional cesarean rate. Specifically, term, singleton, cephalic nulliparous inductions and repeated cesarean deliveries were the major contributors to an increased institutional cesarean delivery rate.

In light of the continuing debate regarding the safety of vaginal birth after previous cesarean delivery, avoiding the primary cesarean delivery is desirable. In this context, objective application and analysis of the singleton, cephalic nulliparous cohort is important. A number of groups have demonstrated inter-institutional variations in nulliparous term singleton vertex cesarean delivery rates.13,14 Nulliparous term singleton vertex comprises only patients delivering between 37 and 41 weeks of gestation, whereas term, singleton, cephalic nulliparous women include all women of 37 completed weeks or more. This constitutes an important difference, because induction of labor after 41 completed weeks is associated with higher risks of dystocia, meconium-stained amniotic fluid, and cesarean delivery.15,16 In addition, nulliparous term singleton vertex excludes intrapartum malpositions, such as face and brow presentations, which almost always require cesarean delivery among nulliparous women.

Term, singleton, cephalic nulliparous induction in particular requires specific consideration. These data demonstrate that increasing singleton, cephalic nulliparous inductions will inevitably lead to a continuing increase in institutional cesarean delivery rates. Although the aim of labor induction is to achieve a safe vaginal delivery for mother and baby, we have previously demonstrated that group 2 (prelabor cesarean delivery and induced term nulliparous women) cesarean delivery rates are universally high, ranging from 30% to 40%, and demonstrate limited variation between centers.8 Our data suggest that expectant management of nulliparous women could lead to lower institutional cesarean delivery rates, contrary to a recent systematic review that compared elective induction at 41 weeks of gestation to expectant management and concluded that elective induction at 41 weeks would lead to a decrease in cesarean delivery rates.17

The major strength of this study is that, although methods and criteria for induction of labor have changed during the period examined, the management regimen in spontaneous first labor has remained essentially unchanged. In addition, we have demonstrated the pertinence of the application of 10-group classification in longitudinal analysis of intra-institutional cesarean delivery trends.

A number of variables that have been associated with higher cesarean delivery rates such as body mass index18 and maternal age19 were not included in our analysis. Reliable information regarding the indications for induction or cesarean delivery was not available, although such data are now being collected prospectively in our unit. Although perinatal mortality or morbidity data were not included in this study, Foley et al have previously demonstrated that our institutional perinatal outcome in nulliparous women at term remained relatively static (average 4.3 deaths 1,000 births) between 1989 and 2000.20 It should also be noted that although we confirmed our previous findings describing the inverse relationship between the group 1:2 ratio and the institutional cesarean delivery rate,8 group 2 combined nulliparous term inductions and nulliparous term prelabor cesarean deliveries. Throughout the study period, the contribution of nulliparous prelabor cesarean deliveries to the institutional cesarean delivery rate remained low; the effectiveness, however, of this ratio in a center with a high nulliparous prelabor cesarean delivery rate requires further validation.

Application of this 10-group classification demonstrates the relatively small absolute contributions of breech delivery, multiple pregnancy, and preterm deliveries to the total institutional cesarean delivery rate and that these rates have remained relatively constant over the past 35 years despite much attention within the obstetric literature addressing the timing and mode of twin deliveries,21 vaginal breech delivery,22 and the optimum management of preterm, growth-restricted fetuses.23 These findings further emphasize our previous assertion that increased emphasis should be placed on the management of term, singleton, cephalic nullipara, a cohort that has been relatively neglected hitherto by research initiatives8 but which has a significant impact on cesarean delivery rates within any obstetric population.

Analysis of term, singleton, cephalic nulliparous women should allow more objective inter-institutional comparison and longitudinal intra-institutional examination of cesarean delivery rates. Examination of the different term, singleton, cephalic nullipara components (spontaneous labor, induction, or prelabor cesarean delivery) can help to identify major variations in practice between institutions. In our hospital, labor induction was the principal contributor to the increasing term, singleton, cephalic nulliparous cesarean delivery rate, whereas significant variations can occur in the management of term, singleton, cephalic nulliparous spontaneous labor8 and in the incidence of nulliparous prelabor cesarean delivery.24 Term, singleton, cephalic nulliparous cesarean delivery rates, together with other significant perinatal and maternal outcomes in this cohort, should thus be considered when auditing individual maternity units. The contribution of spontaneous, induced, and prelabor cesarean deliveries within the cohort can then be highlighted, so as to facilitate comparative intervention strategies.

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© 2011 by The American College of Obstetricians and Gynecologists.

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