A mammogram is a low-dose X-ray used to screen for or diagnose breast cancer, involving the compression of breast tissue to capture internal images. While not strictly forbidden during nursing, routine screening mammograms are generally avoided because the physiological changes of lactation severely compromise image accuracy. The challenge is diagnostic, as the altered breast structure makes reliable interpretation difficult for a radiologist.
Physiological Changes During Lactation
The breast undergoes profound hormonal and structural changes to prepare for and sustain milk production. Under the influence of hormones like prolactin, the breast tissue shifts from predominantly fatty and connective tissue to highly active milk-producing glandular tissue. This process involves a significant increase in the size and number of milk-producing lobules and ducts. This massive expansion of the glandular components leads to a substantial increase in breast density. This increase in density and volume is also accompanied by a rise in blood flow and fluid content within the breast. These temporary changes fundamentally alter the organ’s internal structure, creating a uniform, dense environment that creates significant technical hurdles for mammographic imaging.
Why Accuracy is Compromised
Mammography relies on the contrast between dense tissue and less dense, fatty tissue to distinguish potential abnormalities. On an X-ray image, less dense fatty tissue appears dark, while dense glandular tissue and potential tumors both appear white. During lactation, the entire breast becomes uniformly dense and white on the mammogram, a phenomenon often referred to as a “whiteout” or masking effect.
This high, uniform density drastically lowers the sensitivity of the mammogram, reducing its ability to detect cancer. A small cancerous mass that might have been visible in a non-lactating breast can be completely obscured by the surrounding, dense, milk-filled tissue. This masking increases the risk of a false negative result, where an existing tumor is missed.
The dense tissue can also mimic the appearance of a mass, leading to a higher rate of false positive results. Normal engorged ducts, lactating adenomas (benign tumors common during this period), or milk-filled cysts (galactoceles) can all appear as suspicious white spots. These false positives may necessitate further, potentially unnecessary procedures like biopsies. For this reason, screening mammograms are often deferred until the breast tissue returns to a non-lactating state.
Safety Concerns Regarding Radiation
A common secondary concern for nursing individuals is whether the low-dose radiation from a mammogram could harm the baby through the breast milk. The amount of radiation used is very low and is directed only at the breast tissue. The radiation is localized and does not make the breast milk radioactive. Medical organizations confirm that the X-ray energy used does not accumulate in the milk or pose any risk to a nursing infant. Therefore, the procedure is considered safe for the infant, and there is no requirement to pump and discard milk after the test.
Alternative Screening Methods and Timing
When a palpable lump or other concerning symptom is discovered while a person is nursing, diagnostic imaging should not be delayed. The preferred initial method is typically a breast ultrasound. Ultrasound uses sound waves instead of radiation and is highly effective at differentiating between solid masses, which are more concerning, and fluid-filled structures like galactoceles or simple cysts, which are common and benign during lactation.
If a solid mass is identified, a diagnostic mammogram may be performed in conjunction with the ultrasound, often after the person has pumped or nursed immediately before the exam to temporarily reduce the breast density. For routine, baseline screening, the current medical advice is to wait until the process of nursing has ended and the breast tissue has had time to normalize.
This waiting period is generally recommended to be at least three to six months after the last nursing or pumping session. This allows the glandular tissue to fully involute and the breast density to decrease, which significantly improves the clarity and reliability of the mammogram.