WELLFLEET — Dense breast tissue — which about 50 percent of all women and 40 percent of women over age 40 have, according to the National Cancer Institute — can make breast cancer detection more difficult. And more costly. There are changes in the law and advances in technology that are changing those realities — though they are coming slowly to Cape Cod.

While the Affordable Care Act requires most private health insurers to cover mammograms at no cost to patients, traditional mammograms, such as those available at Outer Cape Health Services, are not as effective at detecting cancer as those done on newer 3D equipment.

That’s because 2D mammography shows both fibrous, dense breast tissue and cancer as white. “So it is like looking for a snowball in a snow field,” said Connecticut Congresswoman Rosa DeLauro, who is sponsoring federal legislation, the Find It Early Act. The law would require insurers to cover the additional tests often needed by women following inconclusive standard mammograms.

Right now many women with dense breast tissue must pay for follow-up screening — usually ultrasounds and sometimes MRIs — because it is not covered by insurance. Even though these tests are done for screening purposes, they are classified by insurance companies as diagnostic tests.

“I think we should revolt, get some women together,” said Cheryl Bartlett of South Yarmouth, the former commissioner of the state Dept. of Public Health.

Bartlett, who is now CEO of the Greater New Bedford Community Health Center, said she has good insurance. Yet because of her dense breast tissue, she has paid anywhere from $300 to $1,100 a year for follow-up screening including ultrasounds and 3D mammography.

“I was a little offended because it is preventive,” Bartlett said. “Screenings are supposed to be free.” And looking at it from the insurers’ perspective, an early diagnosis would save money, she added.

It also saves lives. Studies show that regular mammograms correlate to better overall survival rates. “From my standpoint, if you need it, that additional screening should occur at no additional cost,” DeLauro said.

The issue of dense breast tissue has been in the news since television journalist Katie Couric’s early-stage breast cancer was detected in June. She has dense breasts, and the cancer was found thanks to the addition of an ultrasound to her mammogram screening. The out-of-pocket cost for the additional screening is not going to break Couric’s bank. But paying hundreds of dollars a year could deter many from taking this potentially life-saving step.

Breast density not only makes cancer harder to detect, it raises the risk of cancer. Doctors are not certain why this is so, though the detection problem itself may be the issue, according to the National Cancer Institute. That is why 38 states, including Massachusetts, require women to be notified if they have dense breast tissue.

The work to win notification requirements began with Nancy Cappello of Connecticut, who died in 2018 at age 66 of breast cancer. She and her husband founded Are You Dense?

In 2019, DeLauro got a similar national law passed, but the Food and Drug Administration sat on its implementation for three years, she said. Just last month, however, the FDA agreed to a rollout by early 2023.

The next front line will form on the insurance battlefield, DeLauro said.

Right now, said Lori Jewett, the chief operational officer at Cape Cod Healthcare, “The only exam that is considered preventive by insurers is a screening mammogram.”

Additional mammograms, follow-up ultrasounds, and breast MRIs are considered supplemental exams by insurers and therefore “diagnostic”; they often count towards a deductible and are subject to a co-pay. The out-of-pocket expense to patients varies by insurance carrier and plan, Jewett said.

Cape Cod Healthcare provides 3D mammography. If you have that as your first screening, Jewett said, some insurers will cover it as the preventive annual exam.

The 3D machine is a more accurate tool for women with dense breasts than the 2D. It does not always eliminate the need for additional imaging, Jewett said, but it can greatly reduce it.

In the two months ending Oct. 21, Cape Cod Healthcare did 3,372 screening mammograms at Cuda Women’s Health Center in Hyannis and Fontaine Medical Center in Harwich, Jewett said. Dense breast tissue was found in 40 percent of those tests. But with the 3D results, only 163 of the tests — less than 5 percent — required a follow-up “diagnostic” mammogram and ultrasound.

Outer Cape Health Services is working to replace its 10-year-old 2D machine with a 3D model. It has a $250,000 federal grant for the acquisition, but the new machine costs about $400,000, said OCHS spokesman Gerry Desautels.

There are two bills before the Mass. legislature that would require follow-up screenings to be covered by insurance, Jewett said. An Act Relative to Insurance Coverage for Mammograms and Breast Cancer Screening was introduced in 2019 by Sen. Joan Lovey of the Second Essex District (Beverly, Peabody, and Salem) and Sen. Patrick O’Connor of the Plymouth and Norfolk District. There is a similar bill in the House.

Meanwhile, Cape Cod Healthcare offers financial assistance through the Cape Cod Women’s Cancer Prevention and Early Detection Fund, which was created four years ago to cover the costs of diagnostic testing of women’s cancers not covered by health insurance. The fund provides assistance regardless of income. To get an application, call 508-957-1700.