Also known as breast tomosynthesis

A mammogram is a low-dose x-ray of your breast tissue. It can show changes and abnormalities in your breasts before anything can be seen or felt.

Why is it done?

A mammogram is the best available test to detect small cancers at an early stage when there is a very good chance of successful treatment.

  • Screening mammograms cannot prevent development of breast cancer, but are thought to reduce the chance of dying from breast cancer by approximately a third.
  • Mammograms are most useful in women 50 years and over if done every two years.
  • They can detect about 75% of unsuspected cancers in women under 50 and 85% in women over 50.
  • Mammograms are safe because only very small amounts of radiation are used in two-yearly screenings.

Who is it for?

undefinedIt is recommended that all women aged 45 and over have screening mammograms every two years. In New Zealand, you are able to have a free mammogram every two years for women in the 45 to 69 eligible age range with BreastScreen Aotearoa (Freephone 0800270200).

If you live elsewhere, check with your family doctor for options.

How accurate are mammograms?

Like other screening tests, mammograms are not perfect.

A mammogram may suggest that something is not right when, in fact, all is well. This is called a false positive result.

You may notice symptoms of breast cancer between your two-yearly screening tests. This is called an interval cancer and can happen because:

  • Some cancers do not show up on a mammogram. This is more likely in women before the menopause who often have dense breast tissue. The density usually reduces as women age and go through menopause.
  • The radiologists looking at the mammogram may miss the cancer. This will happen sometimes, no matter how experienced the radiologists are.
  • Sometimes a fast growing cancer will develop.

Despite this, mammograms are the only proven way for finding breast cancers early enough to reduce your risk of dying of breast cancer.

What women aged 45 to 69 should know about mammograms

Regular mammograms reduce the chance of dying from breast cancer among women aged 45 to 69. However, the benefit is greatest for women aged 50 to 69 years for two reasons:

  1. Breast tissue is denser in women under 50. This can make it more difficult to see a cancer. This means about a quarter of cancers in women under 50 years are not detected.
  2. False positive results are also more common in younger women (under 50) and could lead to more unnecessary tests and anxiety.

Preparing for your mammogram

Because you will need to undress from the waist up, wear clothing that is easy to remove, such as a blouse or jersey. A cape or gown will be available where you have your mammogram and every care will be taken to ensure your privacy.

Don't use talcum powder, creams or deodorants on the day of your mammogram as these make cancers harder to find on the mammogram.

You may wish to bring:

  • any previous mammograms that you have
  • your glasses if you need them for reading as you will need to fill in a form
  • a support person or member of your whanau.

Having your mammogram

During the procedure, each breast in turn is held between plates on the mammography machine while the pictures are taken. While this may be mildly uncomfortable, it only takes a few seconds for each picture to be taken.

The radiographer will want you to be as comfortable as possible. Discuss any concerns with them.

The whole visit, including waiting time and breast screening time, is usually about 30 minutes.

The results of the mammogram will be sent directly to you. They will also be sent to your doctor if you have agreed to this.


Only a very small amount of radiation is used in mammography so the radiation risk is extremely low.

Like many tests, there is a small false negative rate. This means mammography is not able to pick up all cases of breast cancer. Likewise, there is a false positive rate which means not all abnormal mammograms turn out to be breast cancer. Further tests will be done to find out if any breast changes are serious or minor.

Learn more

BreastScreen Aotearoa TimetoScreen, National Screening Unit, (Freephone 0800270200).
Enrol online for a free breast screening mammogram Breast Screen Aotearoa, TimetoScreen, National Screening Unit
Breast cancer Ministry of Health NZ

Credits: Credits: Adapted from Breast Screen Aotearoa, Updated by Health Navigator NZ August 2015. Image from