The recommendations from the American College of Obstetricians and Gynecologists (ACOG) will add to the debate over when screening should start, and how often it should be done, based on the chances of catching an early cancer and the risks inherent in any screening.
"We believe it is our job to help women make the best health decision for themselves," said Dr. Jennifer Griffin of the University of Nebraska Medical Center in Omaha, one of the authors of the new recommendations.
Other organizations such as the American Cancer Society and the National Comprehensive Cancer Network recommend that women start getting the breast scans at age 40.
But the U.S. Preventive Services Task Force, a federally -supported expert panel, said in 2009 that screening before 50 should be an individual decision because the benefit is very small compared with the risks. Even at age 50, it only recommended screening every other year.
Any screening decision is about balancing the benefits and harms of a test, said Dr. Michael LeFevre of the USPSTF.
One in eight women will get breast cancer during her life, experts agree. For every 1,000 women who are 40 years old, LeFevre said, 30 would be expected to die of breast cancer if they never have a mammogram.
If those 1,000 women are screened every other year between age 50 and 75, that number drops to 23 deaths. Starting screening in the same group at 40 would save one additional life, meaning 22 would die of breast cancer, on average.
But, LeFevre told Reuters Health, "that small benefit comes with a significant false positive rate, which results in additional testing, including unnecessary biopsies and associated pain and anxiety."
Half of women screened annually in their 40s will have a false alarm on a mammogram, he said, meaning the test shows something suspicious that turns out to be harmless. Follow-up biopsies can be painful, expensive and carry a small risk of infections or other adverse effects.
With his patients, LeFevre said, "my bottom line is that I will discuss mammography at age 40, I will recommend and encourage at age 50 and I will strongly encourage at age 60."
He added that screening every other year, instead of annually, gives women most of the benefit of yearly mammograms, but significantly cuts back on the risk of harm.
The new guidelines only apply to women who are at average risk of breast cancer -- not those with a gene that predisposes them to the disease, for example.