Mammograms dont come into the routine screening for most mothers who are breastfeeding but may sometimes be recommended for those with a family history or where there is a breast lump which needs to be investigated. Usually ultrasounds are preferred as they are easier to interpret but I this question came up on the Facebook page.
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A mammogram is an X ray and breastfeeding as normal can be resumed immediately after the procedure. If a lump is found on the mammogram and further investigation is necessary you can feed as normal after fine needle aspiration. The local anaesthetic does not get absorbed from breastmilk. Some clinicians have been concerned that the proximity of the injection of local to the milk ducts affects the absorption, but it cannot affect the pharmacokinetics of the drug which remains poorly orally bioavailable and with a short half-life.
During breastfeeding breast tissue is denser than usual and can make the results of the mammogram harder to interpret and may need to be seen by an expert to interpret the results. The density is also affected by the frequency of breastfeeding and the stage of lactation.
During the procedure the breasts are squeezed between 2 metal plates to “flatten” them as much as possible. This may of course result in leakage of milk so feeding just before the mammogram or expressing milk as much as possible may help. The leakage should not be a source of embarrassment to either the patient or technician.
Some breast experts recommend an ultrasound or MRI which can be easier to interpret.
The 2023 guidelines from the NHS https://www.gov.uk/government/publications/breast-screening-higher-risk-women-surveillance-protocols/protocols-for-surveillance-of-women-at-higher-risk-of-developing-breast-cancer#screening-women-in-pregnancy-and-lactation state:
“Screening with mammography can be safely performed during pregnancy but as mammographic density increases during pregnancy and lactation, its effectiveness is reduced. Women can be screened during lactation but are advised to breastfeed or express milk prior to the examination. Shielding is not considered necessary due to the low radiation dose of mammography.”
Needle biopsy
There appears to be a concern from some clinicians that a needle biopsy may result in a milk fistula. The risk of milk fistula, which is chronic milk leakage, is very rare. There is no research on the incidence of milk fistulas with biopsies, but it is reported to be rare.
Other sources of information
La Leche League Lumps and Mammograms
NHS breast screening: Helping you decide https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/440798/nhsbsp.pdf
