A bilateral mammogram is simply a mammogram that images both breasts. “Bilateral” is medical terminology for “both sides,” so when you see this phrase on a doctor’s order or an insurance statement, it means X-ray images were taken (or will be taken) of your left and right breast. This is the standard approach for nearly every mammogram, whether it’s a routine screening or a closer look at a specific concern.
Why Both Breasts Are Always Imaged
If you have both breasts, your mammogram will almost always be bilateral. Imaging both sides allows radiologists to compare the tissue, density, and structure of one breast against the other, making it easier to spot anything unusual. Asymmetries between the two sides can be an early clue that something needs a closer look, even when each breast might appear normal on its own.
A unilateral mammogram (imaging just one breast) is rare and typically reserved for someone who has had a mastectomy on one side or who recently had a full bilateral mammogram within the past year and only needs follow-up on one breast.
Screening vs. Diagnostic Mammograms
Both screening and diagnostic mammograms are usually bilateral. A screening mammogram is a routine check done when you have no symptoms. It captures two standard views of each breast, one from top to bottom and one from side to side, for a total of four images. The whole appointment typically takes less than 30 minutes.
A diagnostic mammogram is ordered when something specific needs investigation: a new lump, breast pain, nipple discharge, or skin changes. It may include additional views or magnified images of a particular area. Even though the concern might be on one side, a diagnostic mammogram is still usually bilateral so the radiologist can compare both breasts.
What Happens During the Procedure
A technologist will position one breast at a time on a flat surface attached to the X-ray machine. A compression paddle gently presses down to spread the tissue evenly, which improves image quality and keeps the radiation dose low. An X-ray is taken, then the machine is repositioned to capture a second angle. The process is then repeated for the other breast.
Compression lasts only a few seconds per image but can be uncomfortable, especially if your breasts are tender. Scheduling your mammogram for a time when your breasts are least likely to be sore (typically a week or two after your period starts) can help. You’ll also want to skip deodorant, antiperspirant, and powders on the day of the exam, since particles from these products can show up on the images and mimic abnormalities.
2D vs. 3D Mammography
Your bilateral mammogram may be performed with traditional 2D imaging, 3D imaging (called tomosynthesis), or a combination of both. In 3D mammography, the X-ray arm sweeps in a short arc around the breast, capturing thin slices that the computer assembles into a layered image. This makes it easier to see through overlapping tissue.
Studies consistently show that 3D mammography catches more cancers than 2D alone and reduces the number of false alarms that lead to unnecessary callbacks. The benefit holds across different breast densities and age groups, though some research has found the improvement in detection is especially notable in women aged 60 to 69. Many screening centers now use 3D as the default, but if you’re unsure which type you’re getting, it’s worth asking.
When to Start and How Often
The U.S. Preventive Services Task Force recommends bilateral screening mammograms every two years for all women starting at age 40 and continuing through age 74. This recommendation applies to people at average risk and includes cisgender women, transgender men, and nonbinary individuals assigned female at birth. If you have a family history of breast cancer or other risk factors, your doctor may suggest starting earlier or screening more frequently.
Understanding Your Results
Mammogram results are reported using a standardized scoring system called BI-RADS, which ranges from 0 to 6. Here’s what each category means in practical terms:
- BI-RADS 0: The images weren’t complete enough to make a call. You’ll be asked to come back for additional views or an ultrasound.
- BI-RADS 1: Negative. No signs of cancer.
- BI-RADS 2: Also normal, but the radiologist noted a benign finding like a cyst. No cause for concern.
- BI-RADS 3: Probably normal, but a follow-up mammogram in six months is recommended to make sure nothing changes.
- BI-RADS 4: Suspicious. There’s roughly a 23% to 34% chance the finding is cancerous, and a biopsy is recommended.
- BI-RADS 5: Highly suggestive of cancer, with about a 95% likelihood. A biopsy is strongly recommended.
- BI-RADS 6: Used when cancer has already been confirmed by a prior biopsy.
Getting called back for extra images (a BI-RADS 0 result) is common and doesn’t mean cancer is likely. It often just means the radiologist wants a clearer picture of a particular area.
Coverage and Cost
Under the Affordable Care Act, most health insurance plans must cover preventive screening mammograms with no copay, deductible, or coinsurance when you use an in-network provider. Because the USPSTF gives screening mammography a “B” grade, it falls squarely under this requirement. If your mammogram is diagnostic rather than screening, cost-sharing rules may differ depending on your plan, so checking with your insurer ahead of time can help you avoid surprises.