For female patients, operation outcomes tend to be significantly better when their surgeon is also female, recent research out of Canada has found.

No one really knows why that is just yet, but a new model comparing the sex of the surgeon, the sex of the patient, and the outcomes of the surgery have now revealed an implicit bias that could be costing patients their health and even their lives.

The data is based on more than 1.3 million patients who underwent one of 21 common elective surgeries in Ontario, Canada between 2007 and 2019.

Overall, the analysis suggests that when a male surgeon treats a female patient, that patient is 16 percent more likely to experience complications, 20 percent more likely to remain in the hospital for longer, and 32 percent more likely to die than if they were treated by a female surgeon.

On the other hand, male patients treated by a female surgeon were only 2 percent more likely to experience complications, and 13 percent less likely to die than if they had seen a male surgeon.

The underlying reason or reasons for this discrepancy in care remains unclear, but this isn't the first time a study has found a patient's sex might impact how their doctor treats them.

In 2018, female patients in Florida hospitals who were seeking care for heart attacks were found to have higher mortality when treated by male physicians.

In comparison, female physicians had more consistent outcomes no matter whether their patient was male or female.

Interestingly, male surgeons who had more exposure to female physicians and female patients had better outcomes for women.

While some past studies suggest female physicians prescribe different follow-up tests and medications compared to male doctors, or that they listen more to their patients, further research is needed to determine which factors are influencing these outcomes the most. Once we can figure that out, we can start to mend the bias.

"Surgeons likely believe they provide the same quality of care to patients irrespective of identity," reads an invited commentary to the current paper, written by surgeons Amalia Cochran and Andrea Riner at the University of Florida College of Medicine.

"However, these data underscore an under-appreciated phenomenon and highlight a measurable repercussion of implicit bias. Metrics of surgeon outcomes with regard to patient identity should be developed and incorporated into performance reviews."

Medical experts could also be better trained to improve their care and communication with patients, especially those with identities different from their own, Cochran and Riner suggest.

While most findings to date suggest patients are generally better off in the hands of female surgeons and physicians, the significant gender disparity in these professions means many patients don't ever get to make that choice.

In 2020, slightly more than 27 percent of general surgeons in Canada were female. In the United States, the percentage is slightly lower. In both nations, female surgeons are paid significantly less than their male counterparts.

"Female patients with surgical disease should not be disadvantaged because there simply are not enough female surgeons or surgeons who are competent in the care of female patients," the commentary concludes.

"While data are lacking, the concerns faced by female patients undergoing surgery may be even greater for gender-nonconforming and transgender patients. We owe it to patients to provide them with the best outcomes, regardless of how their identities may align with ours."

The study was published in JAMA Surgery.