Last year, for instance, a blue-ribbon panel recommended they start at age 50.
The U.S. Preventive Services Task Force concluded that women at average risk for breast cancer don't need mammograms in their 40s and should get one just every two years starting at 50.
The World Health Organization estimates that mammograms reduce the breast cancer death rate by 25 percent in women over 50. Other groups put the figure at 15 to 23 percent.
Special Section: Dr. Jennifer Ashton
Dr. Jennifer Ashton's Twitter page
Just last week, a study out of Norway suggested .
Now, says CBS News Medical Correspondent Dr. Jennifer Ashton, a new study of one million patients suggests that women in their 40s who have the exams can significantly cut their risk of dying of breast cancer.
The newest research is out of Sweden. It was, says Ashton, a practicing obstetrician/gynecologist, "a very large study, over a million women, did have its limitations, like every study. However, it found that women in the 40 to 49-year-old age group who had mammograms reduced their risk of dying of breast cancer by 26 percent.
"Again, I do not think this is a game changer; this is just another in the battle, ongoing debate over mammograms' pros and cons."
"But it is," observed "Early Show" co-anchor Maggie Rodriguez, "in keeping with what we had heard for much of the time - that women in their 40s should have mammograms. And then, last year, this preventive task force changed it to 50. Why did they change it to begin with?"
"A lot of it has to do with science," Ashton explained. "Mammography is not a perfect screening test. It has a lot of limitations involved. It has false positives -- in other words, it can find things … that turn out not to be cancer. It has false negatives, meaning it can give you a normal result and there can still be a cancer there. Obviously, there's cost involved.
"It's not a perfect test. But right now, it really is the best imaging/screening test we have. And last year, the reason the preventive service task force said it might not be so great or even recommended in women in their 40s really comes down to numbers. It comes down to statistics. And this study actually was in keeping with that. It showed that, in order to save one life, over 1,200 mammograms would need to be done every other year for a ten-year period for women in their 40S. Now, the hard-core statisticians and scientists will say, well, those numbers do not support its use in this age group.
"But, for women who are that one life or for doctors like myself who sit across from a patient and say, 'You might be the one,' or 'I don't want to miss the one cancer in you, my one patient,' emotion comes into play. And medicine is a science, but it's also an art, so you have to take into account science, statistics, numbers; you also have to take into account emotion. There's no getting around it."
So would Ashton recommend that her patients get mammograms, just in case? And will health care reform result in more women getting them?
"In medicine," Ashton responded, "in science, we don't want to do things just in case. We really do want to go back on evidence, and do risks and benefits balance each other out? And are the pros and cons in keeping with whatever we're recommending?
"For low-income women, mammography is not as accessible as we would like. So, that is a target population that, yes, we hope, with the new health care reforms, those women will have mammography or other screening tests available to them.
"And I can tell you that, with anything that changes this quickly, most doctors and most women will stay the course for now and not make any sweeping changes."