Elderly hospital patients may be less likely to die prematurely or be readmitted for serious complications when they're treated by female physicians, a U.S. study suggests.

With female doctors, patients had 4 percent lower odds of dying within a month after being admitted to the hospital and a 5 percent smaller chance of repeat hospitalizations within the first month after leaving the hospital, the study found.

"The difference in mortality rates surprised us," said lead author Dr. Yusuke Tsugawa, a health policy researcher at Harvard University in Boston.

Previous studies have found differences in the way men and women practice medicine, Tsugawa added by email. For example, female physicians are more likely to adhere to clinical guidelines and focus more on communication and forging relationships with patients.

"However, it was largely unknown whether such differences have a meaningful impact on patient outcomes," Tsugawa said.

While the findings don't necessarily mean patients need to seek out female doctors, the results do suggest there's room for some physicians to rethink how they communicate with patients and make treatment decisions, Tsugawa said.

To assess differences in outcomes for male and female doctors, researchers analyzed data on more than one million adults 65 and older insured by Medicare who altogether were hospitalized more than 1.5 million times between 2011 and 2014. During those hospital stays, they were treated by general internists.

The research team analyzed 30-day mortality rates - i.e., how many patients died within 30 days of being admitted to the hospital - and 30-day readmission rates, or how often patients returned to the hospital within 30 days of discharge.

During the study period, 58,344 internists treated at least one hospitalized Medicare patient. Among this group of doctors, 18,751, or 32 percent, were women.

After adjusting for patient and physician characteristics, there were small but clinically meaningful differences in mortality and readmission rates, researchers report in JAMA Internal Medicine.

Patients treated by female physicians had 30-day mortality rates of 11.07 percent, compared with 11.49 percent for male doctors, the study found.

With female doctors, patients had 30-day readmission rates of 15.02 percent, compared with 15.57 percent for male physicians.

Researchers saw better outcomes for mortality and readmissions with female physicians across a range of common conditions treated in the hospital including bloodstream infections, pneumonia, congestive heart failure, chronic obstructive pulmonary disease, urinary tract infections, kidney failure, heart rhythm disorders and gastrointestinal bleeding.

The study is observational and doesn't explain why there might be better outcomes with female doctors, the researchers note. It's possible that gender serves as a marker of differences in practice patterns that might influence outcomes, they say.

Still, the findings that female internists provide higher quality care should push hospitals to do a better job of promoting and paying women, who typically earn less and have fewer opportunities for advancement than their male peers in medicine, Dr. Anna Parks and Dr. Rita Redberg of the University of California, San Francisco, argue in an accompanying editorial.

"Some have suggested that home responsibilities might contribute to female physicians providing inferior care and thus justify these disparities," Parks said by email.

"The data from this paper should serve to highlight these inequities - female physicians provide equivalent or potentially better care compared to male colleagues yet get promoted less often and have lower salaries than their male colleagues," Parks said. "We want to close that gap."