Caesarean sections are longer and more expensive in obese women


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The Methods and Implementation Support for Clinical and Health Research platform helped researchers investigate the link between maternal weight and the duration and costs of caesarean sections. The findings can help hospitals improve surgery schedules and resource management.

The outcome

The time that a mother spends in the operating room, in surgery, and under anaesthesia for a caesarean section increases with her body-mass index (BMI). Longer times for caesarean sections lead to higher costs for hospital admission. These findings are the result of a study supported by the Methods and Implementation Support for Clinical and Health Research (MISCH) platform. The MUM SIZE study found that Australian hospitals will need to spend an extra $AU50 million over the next 10 years to care for super-obese women (BMI over 45 kg/m2) undergoing caesarean sections.

The MUM SIZE study involved 1457 participants in seven hospitals that are affiliated with the University of Melbourne. The hospitals were The Royal Women’s Hospital, The Northern Hospital, The Mercy Hospital for Women, The Western Hospital, Ballarat Base Hospital, Goulburn Valley Hospital and Wangaratta Base Hospital.

The added times associated with maternal obesity are relevant to health service planning. The MUM SIZE findings can help hospitals improve how they schedule surgeries, book operating rooms and allocate resources.

The need

Obesity is increasing. About 13 per cent of the world’s population was obese in 2016, according to the World Health Organization. The worldwide prevalence of obesity almost tripled from 1975 to 2016.

More women of reproductive age are obese. And more women are exceeding the recommended weight gain during pregnancy. The rate of caesarean sections is also increasing, particularly for obese women.

There has been considerable research into how maternal obesity affects the health of both mother and child. But there was little information on the relationship between obesity and the time it takes to perform a caesarean section. Anecdotal reports suggested that caesarean sections take longer for obese women, but hospitals needed robust data to change practice.

The solution

Associate Professor Alicia Dennis is an expert in obstetric anaesthesia and an anaesthetist at The Royal Women’s Hospital. Professor David Story is the Foundation Chair of Anaesthesia in Melbourne Medical School and an anaesthetist at Austin Health. Along with colleagues from University-affiliated hospitals, they wanted to test the hypothesis that maternal weight affected the duration, and thus the cost, of a caesarean section.

The research team approached the MISCH platform for help. The MISCH team includes experts in biostatistics, clinical epidemiology, health economics and health informatics. They helped the researchers to design and run an observational study. In this type of study, researchers make observations in a specific setting without trying to influence the outcome. (By contrast, researchers use experimental, or interventional, studies to test the effects of an intervention, such as a drug treatment.)

The MISCH team provided advice on the type and amount of data to collect. This included the time spent in the operating room, in surgery and under anaesthesia. It also included the medical costs associated with each study participant’s hospital visit. The costs covered supplies, staffing and related services.

MISCH staff built and managed a database to store data securely throughout the study. They used Research Electronic Data Capture (REDCap) software, which is widely used by the academic research community. The database was designed to allow participating hospitals to access and deposit data themselves.

The MUM SIZE study ran from 23 November 2013 to 2 February 2015. Data was collected for at least three months from women at each of the seven hospitals. MISCH staff analysed the clinical and economic data for each BMI group.

The researchers defined super-obesity during pregnancy as a BMI over 45 kg/m2. They defined normal weight during pregnancy as a BMI of 23.5 to <30 kg/m2. These values are 5 kg/m2 more than the BMI values defined by the World Health Organization. This is to account for weight gained during pregnancy.

The MUM SIZE study found that super-obese mothers spent 27 per cent more time in the operating room than mothers of normal weight. This translated into a 22 per cent increase in operating-room costs. Super-obese mothers also spent 20 per cent more time in surgery and 40 per cent more time under anaesthesia. The costs of pathology services were 55 per cent higher for super-obese mothers compared with mothers of normal weight. Overall, the total cost of hospital admission for caesarean section was 15 per cent more for super-obese mothers.

The platform

The Methods and Implementation Support for Clinical and Health Research platform provides expert advice in biostatistics, health economics, health informatics and clinical trial governance. It also provides operational support for all stages of health-related research, from developing protocols and designing experiments to analysing experimental results and providing information for grant applications.

The support provided in this project included:

  • Biostatistical analysis – helping to design the study, including calculating the required number of samples and refining the study protocols; developing and refining the forms used for data collection; performing database checks and data cleaning; analysing data using linear regression; and interpreting study findings.
  • Health economics – performing cost analyses using patient-level data extracted from hospital administrative records.
  • Health informatics – configuring a REDCap database to support data collection directly from participating hospitals. MISCH is a member of the REDCap consortium, which gives the platform access to a local REDCap system.



Dennis AT et al (2017) Associations between maternal size and health outcomes for women undergoing caesarean section: a multicentre prospective observational study. BMJ Open 7: e015630. doi: 10.1136/bmjopen-2016-015630

Contact us

If you have a problem that could be solved by the Methods and Implementation Support for Clinical and Health Research team please contact us.

MISCH Manager
+61 3 8344 0643

Banner image: Black and white image of a woman holding her baby after a Caesarean. Image by Jessika Arraes/Pexels.

First published on 25 February 2021.

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