A mammogram not only shows if you have signs of breast cancer.

It also shows how "dense" your breasts are.

In March, the federal Food and Drug Administration updated regulations to require all U.S. mammography centers to notify women about their breast density after a mammogram. Pennsylvania started requiring the reporting in 2014, and WellSpan was doing it even before the state mandate.

There are four categories of breast tissue density: fatty (about 10% of women), scattered fibroglandular (about 40%), heterogeneously dense (about 40%), and extremely dense (about 10%).

These are complex-sounding terms. What do they mean? Why does it matter? What should women do with this information?

"Women should know what their breast density is," says Dr. John Nawa, a WellSpan radiologist. "It is important information that helps to determine their risk level for breast cancer and informs possible next steps in screening."

Here are some facts to help you understand breast density. You have us to help you through your mammogram journey and ensure you are receiving personalized care based on your breast density, age, and risk level.

What is breast density?

Breast density is determined by the tissue makeup of your breasts. Breasts contain three types of tissues:

1. Glandular tissue, which consists of lobules, the small glands that produce milk, and ducts, the tubes that carry the milk from the lobules to the nipple.
2. Fibrous connective tissue, which holds the breast tissue in place.
3. Fatty breast tissue, which fills in the spaces between the other types of tissues.

Breast density is a measure of the first two types of tissue: glandular and fibrous connective (together called fibroglandular). The more of those two tissues you have, the denser your breasts are.

How common are dense breasts?

Nearly half of all women who are age 40 and older who get mammograms have heterogeneously dense or extremely dense breast tissue, according to the National Cancer Institute.

Dense breast tissue can be inherited. It also is more common in younger women, lean women, women who are pregnant or breastfeeding, and women who take hormone replacement therapy.

How can you find out if you have dense breasts?

Breast density is not related to how large or how firm your breasts are. Also, a woman can't tell if her breasts are dense by self-exams. Only a mammogram can determine breast density.

But with that information comes a challenge.

"Because of their makeup, dense breasts are harder to see through on a mammogram, when we are looking for possible tumors," Nawa says. "But we do have technology to help us."

That technology includes 3D mammography, available at all WellSpan mammography sites. Studies have shown it is particularly helpful in evaluating women with dense breasts. 3D mammograms detect 41% more invasive cancers, detect cancers earlier, and reduce false positives. Mammography is a very effective screening tool and, when completed routinely, it can lead to the discovery of the breast cancer as early as possible. Earlier breast cancer diagnosis leads to less treatment and increased survival.

The other technology includes additional, more intensive screening techniques for examining breast tissue.

Do dense breasts impact your breast cancer risk?

Women with extremely dense breasts are four to five times more likely to get breast cancer than women with fatty breasts.

However, breast density does not appear to be related to breast cancer survival. Women with dense breasts are not more likely to die from breast cancer than women with fatty breasts.

What should you do if your mammogram shows you have extremely dense breasts?

An additional, different type of screening may be needed. Talk to your breast health care provider – such as your gynecologist or family practice physician – to determine if this makes sense for you.

Your need for additional screening will depend on your risk factors for breast cancer, such as your age, your family history, and other factors. That screening may include magnetic resonance imaging, a contrast-enhanced mammogram (which includes an injection of X-ray dye), or ultrasound.

"We offer more in-depth screening to fit every woman's needs," Nawa says.

To learn more about WellSpan mammography services, go here. More information on WellSpan 3D mammography is here.