Variation in and factors associated with timing of low risk, pre-labour repeat caesarean sections in NSW, 2008-2011 January 2016, Volume 26, Issue 1

Introduction

Many international obstetric guidelines^1-3, including those of the Royal Australian and New Zealand College of Obstetricians and Gynaecologists ², recommend that low-risk prelabour caesarean sections be performed after 39 weeks gestation, because of the increased risk of respiratory and other adverse infant outcomes when babies are electively delivered before 39 weeks.⁴ In April 2007, the New South Wales (NSW) Ministry of Health released a mandatory policy directive for all NSW public hospitals (PD2007_024), ‘Maternity − timing of elective or pre-labour caesarean section’, requiring that “where there are no compelling medical indications, elective or prelabour caesarean section does not occur prior to 39 completed weeks gestation”.⁵

Although a slight change in timing of prelabour caesarean sections has been observed since 2008⁶, current practice and compliance with the policy directive are unknown. Additionally, the relationship between hospital and patient factors and timing of low-risk caesarean sections has not been explored. This study aimed to explore variation in public hospital rates of early (37−38 weeks) prelabour repeat caesarean section among low-risk women at and beyond term in NSW between 2008 and 2011.

Methods

This study examined routinely collected NSW health data from 2008 to 2011, following the introduction of the policy (April 2007). Data were obtained from two linked Ministry of Health datasets: the NSW Perinatal Data Collection and the Admitted Patient Data Collection. Record linkage was undertaken by the NSW Centre for Health Record Linkage.^7,8 The study population included all low-risk, prelabour caesarean births among women who had had a previous caesarean section (i.e. the indication for caesarean section was elective repeat). The study was limited to repeat caesarean sections to reduce the heterogeneity of populations within and between hospitals. Low-risk pregnancies were defined as singleton live births at term (37−42 weeks) among women without diabetes, hypertension, other chronic diseases or placental conditions, with no previous perinatal death or classical caesarean, and where the indication for caesarean section was ‘elective repeat caesarean section’. Private hospitals (NSW Health policy directives apply to public hospitals) and hospitals with fewer than 50 births per year were excluded. Gestational age (expressed as completed weeks of gestation) was based on the best clinical estimate using ultrasound examination and/or last menstruation period.

Casemix and hospital factors are potentially associated with the timing of elective repeat caesarean sections at term.⁹ The casemix variables available for analysis included maternal age, country of birth, smoking, socio-economic status, body mass index, private healthcare, number of previous caesarean sections, number of previous vaginal births, assisted reproductive technology use, previous noncaesarean uterine scar¹⁰ and infant size for gestational age. Hospital factors included obstetric training provision (primary − referring to tertiary obstetric training hospitals, or secondary − referring to large district and rural hospitals that host obstetric registrars), level of perinatal care (neonatal intensive care unit, continuous positive airway pressure [CPAP] facilities and CPAP-trained staff, other), location and birth volume. Hospital rates of obstetric transfusions, anaesthetic services and low-risk births were also used, as was the rate of vaginal birth after primary caesarean section for breech presentation as an indicator of hospital propensity for vaginal birth after caesarean.^9,11 Variables from the birth record are considered to be reliably reported, and the coding of hospital diagnoses and procedures has previously been validated.^12,14

Using methods detailed elsewhere¹¹, we conducted multilevel regression modelling with the outcome ‘timing of low-risk prelabour repeat caesarean section’ (37−38 weeks was classified as ‘early delivery’, and 39−42 weeks was classified as ‘later delivery’). Briefly, multivariable, multilevel binomial logistic regression models were constructed with a manual backward stepwise approach. An unadjusted model included a random intercept for hospital, to account for clustering of observations from the same hospital, and a shrinkage factor to allow for inclusion of hospitals with small sample sizes. Models were fitted and progressively adjusted, first for casemix and then for hospital factors, as described previously.^9,11 The final risk-adjusted hospital rates with 95% confidence intervals (CI) were plotted. The relative contributions of casemix and hospital factors to the overall reduction in variation were quantified by calculating the difference between the hospital variation of the current and preceding step as a proportion of the unadjusted model’s hospital variation.^9,11 Adjusted odds ratios (aOR) and 95% CI for factors retained in the final model are reported. The study was approved by the NSW Population and Health Services Research Ethics Committee.

Results

Between 2008 and 2011, there were 15 163 prelabour repeat caesarean sections among low-risk women giving birth in NSW public hospitals. This represented 5.3% of all births and 19.5% of all caesareans in public hospitals in this period. Of the 61 public hospitals, 40 (65.6%) were regional, and 33 (54.1%) provided primary or secondary obstetric training. Overall, 34.7% of low-risk prelabour repeat caesarean sections occurred before 39 weeks gestation. The low-risk prelabour repeat caesarean section rate decreased from 35.6% in 2008 to 34.1% in 2011.

Unadjusted hospital rates of low-risk prelabour repeat caesarean section before 39 weeks gestation varied widely (6.1% to 76.6%). Adjusting for casemix factors increased the between-hospital variation by 4.3%, and adjusting for hospital factors reduced variation by 20.0%. The final adjusted model demonstrated considerable variation (16.3% to 67.5%) in hospital rates of early-term low-risk prelabour repeat caesarean section. Overall, compliance with the NSW policy ranged from 32.5% to 83.7%. Twenty (32.8%) hospitals had an adjusted rate that was significantly different from the adjusted mean of 35.4% (Figure 1).

Smoking (aOR 1.18; 95% CI 1.06, 1.31), private healthcare (aOR 1.77; 95% CI 1.59, 1.96), assisted reproductive technology use (aOR 1.68; 95% CI 1.28, 2.21), two or more previous caesarean sections (aOR 1.70; 95% CI 1.58, 1.83), previous vaginal birth (aOR 1.26; 95% CI 1.14, 1.39), a noncaesarean uterine scar (aOR 2.40; 95% CI 1.48, 3.91) and delivering in a hospital with CPAP facilities (aOR 1.23; 95% CI 1.04, 1.47) were associated with higher odds of early delivery. Having infants that were small for gestational age was associated with lower odds (aOR 0.77; 95% CI 0.65, 0.90) of early delivery. Hospitals with higher rates of low-risk deliveries (aOR 0.69; 95%CI 0.57, 0.82) and higher rates of propensity for vaginal birth after caesarean (aOR 0.96; 95% CI 0.94, 0.98) also had lower odds of early delivery.

Figure 1.     Risk-adjusted hospital rates of early (37–38 weeks gestation) low-risk prelabour repeat caesarean section in NSW, 2008–2011 (click to enlarge)

Discussion

The NSW hospital rates of low-risk early-term elective repeat caesarean sections were generally high, with an adjusted average of 35.4%. This rate is similar to a US study that found that 35.8% of early-term elective repeat caesarean sections were performed before 39 weeks gestation.¹⁵ One tertiary-level Australian hospital in Queensland reported a rate of low-risk, early-term caesarean section of 59.9%.¹⁶ Although this single result is high, it is within the range of hospital early-term caesarean section rates found in the current study (adjusted rates from 16.3% to 67.5%) and also similar to rates in some Canadian hospitals.¹⁷

Although other studies have not presented analyses adjusted for casemix and hospital factors, they do report that differences in the rates of elective repeat caesarean sections at early term are major contributors to widely varying overall-term caesarean section rates, ranging from 29% to 57%.^18,19 For this study, despite adjustment for casemix and hospital characteristics, we found persistent, large between-hospital variation in rates of early-term repeat caesarean section, suggesting that nonmedical factors are related to the timing of low-risk, prelabour caesarean section. Patients’ preferences and physicians’ decision making vary, and may explain the remaining variation.²⁰ Another contributing factor may be the challenge of scheduling, which may be logistically difficult for hospitals and women¹⁹, particularly where travel distance to the hospital is long, such as in rural Australian communities. An Australian population cohort study found that, among low-risk women, 8.5% of caesarean sections planned for 39 weeks gestation resulted in an unscheduled caesarean section due to spontaneous labour before 39 weeks.²¹ However, a secondary analysis of a randomised controlled trial found that scheduling a planned caesarean section after 39 weeks gestation led to a 60% increase in unscheduled caesarean sections, and a 70% increase in after-hours deliveries. Such findings have financial and resource implications for hospitals.¹⁹

Our findings suggest generally poor compliance with the NSW Ministry of Health policy directive concerning the timing of elective repeat caesarean sections across NSW public hospitals. Adjusted rates of compliance across NSW ranged from 32.5% to 83.7%. Although it would be unrealistic to assume that all patient care episodes can comply with guidelines, it is unclear what an acceptable compliance rate would be. One study suggests that 5% of elective caesarean sections before 39 weeks would be acceptable²², while another considers that 30% of elective deliveries before 39 weeks is an achievable quality improvement goal, while recognising that the rate should ultimately be lower.¹⁷

Internationally, there has been a concerted effort to reduce the rate of early-term elective caesarean sections, and this rate is one of the maternity quality metrics used in the US.²³ Different approaches to reducing the rate of early-term elective caesarean sections have seen varying levels of success^24,25 with the ‘hard stop’ approach (enforceable prohibition of elective caesarean sections before 39 weeks) being more effective than other approaches.²² Importantly, reducing elective caesarean sections before 39 weeks gestation has been associated with a reduction in neonatal morbidity.²² For NSW, despite state⁵ and national² guidelines recommending elective low-risk caesarean sections at or beyond 39 weeks gestation, large variation in hospital rates for the timing of elective low-risk caesarean section suggests that many NSW hospitals (and possibly hospitals in other Australian states) would benefit from the experience of our international colleagues.

Despite comprehensive, validated population data⁵, this analysis is limited by the availability of clinical information. Reporting practices between hospitals may differ, and confounding by unmeasured clinical and nonmedical factors is possible. Lack of data on elective repeat caesarean section before 2007 precluded looking for differences before and after introduction of the policy.

Conclusion

There appears to be generally poor compliance with the policy for low-risk prelabour caesarean section from 39 weeks gestation in NSW public hospitals. Large between-hospital variation persisted following adjustment, suggesting that nonmedical factors are related to timing of low-risk prelabour repeat caesarean section. Further strategies, such as those implemented internationally, are required to improve adherence to this evidence based policy.

Acknowledgements

We thank the NSW Ministry of Health for access to the population health data and the Centre for Health Record Linkage for linkage of the datasets. This work was completed while KS was a trainee on the Biostatistics Training Program funded by the NSW Ministry of Health. She undertook this work while based at the Kolling Institute of Medical Research. JF is supported by an Australian Research Council Future Fellowship (FT12010069), and CR by a National Health and Medical Research Council Senior Research Fellowship (1021028).

Copyright:

© 2016 Schemann et al. This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International Licence, which allows others to redistribute, adapt and share this work non-commercially provided they attribute the work and any adapted version of it is distributed under the same Creative Commons licence terms.