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Delivery methods

Non-traditional analysis finds C-section rate goes down with OB delivery

Research

By Michelle Osmond

According to the Public Health Agency of Canada, the rate of caesarean deliveries (C-sections) sits at about 28 per cent of hospital deliveries in the country. The World Health Organization puts 10-15 per cent as the ideal rate.

A Canadian Institute of Health Information report from 2011-12 shows that Newfoundland and Labrador sits at 21.1 per cent for first-time moms (the second highest in the country); that rate jumps to 28.5 per cent for women age 35 and older, the highest in the country. Repeat C-sections for the province was also the highest in the country, at 91.5 per cent.

Dr. Amanda Pendergast, Dr. Russell Dawe and Dr. Susan Avery are some of the authors of the study.
From left, the Faculty of Medicine’s Dr. Amanda Pendergast, Dr. Russell Dawe and Dr. Susan Avery are some of the authors of a newly published study about the rates of C-sections.
Photo: Jennifer Armstrong/HSIMS

Given these rates, then, it’s not surprising that many researchers study C-section rates and the reasons behind them.

GPs versus OBs

Previous studies have shown that family doctors have lower or equivalent C-section rates compared to obstetricians.

However, researchers at the Faculty of Medicine used a different method of data analysis and got the opposite result: Fewer C-sections among obstetricians.

The method used by the Memorial research team is known as instrumental variable analysis. In traditional analysis, researchers identify differences between two groups they are comparing, measure those differences and then adjust for those differences in their analysis.

With instrumental variable analysis, the method adjusts for differences that have not been identified. Meaning, if there are unknown differences between the two population groups, the instrumental variable compensates for those differences and supplies a better answer to the researchers’ question.

Essentially, it’s a catch-all solution to variables.

“When we run our same data through the traditional analysis, the results flip again,” said Dr. Russell Dawe, assistant professor, Discipline of Family Medicine, Faculty of Medicine, and principal investigator.

“These conflicting results suggest that there may be clinical or sociocultural factors affecting women’s choice of C-section, which previous studies, including our own, have not accounted for, but which the instrumental variable is able to account for.”

Missing pieces

“The findings suggest that clinical and/or sociocultural factors affecting the decision to perform a caesarean delivery are missing from the research and that there is variability in these factors between women cared for by family physicians and women cared for by obstetricians,” said Dr. Dawe.

Although the researchers did account for the more traditional variables, such as employment rate and visible minority status, among others, Dr. Dawe notes that other clinical or sociocultural factors were not.

These factors could include a partner’s socio-economic status; the health-care team’s culture regarding C-sections; and a patient’s history of post-partum depression or anxiety surrounding a previous C-section which led to a need for control.

Dr. Dawe suggests that a follow-up study is needed to identify other cultural, social or clinical issues impacting C-section rates, with a revised study on rates that include those variables.

The article, Cesarean Delivery Rates among Family Physicians versus Obstetricians: A Population-based Cohort Study using Instrumental Variable Methods, was published Dec. 12, 2017, in the CMAJ Open.

Funding for the study was provided to the research team through the Dr. A.R. Cox Research Grant via the Medical Research Fund at the Faculty of Medicine.


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