Medical Tests While Breastfeeding

Mothers are sometimes told they need to interrupt breastfeeding in order to have certain medical tests, however many medical tests are compatible with breastfeeding. This article shares useful resources to discuss with your health professionals regarding the compatibility of various diagnostic tests while breastfeeding.

Imaging and biopsies

The Academy of Breastfeeding Medicine (ABM) Protocol #301 refers to guidelines from The American College of Radiology (ACR)2 that say all breast imaging studies and biopsies are safe for breastfeeding women.

Is weaning necessary to investigate breast lumps?

Dr Jack Newman, a Canadian paediatrician and breastfeeding expert, states that it is not necessary to wean prior to diagnostic tests on the breast. He says:

A reminder: almost no investigation of the breast (ultrasound, mammogram, CT scan, MRI scan, needle biopsy, core biopsy, etc.) requires a mother to stop or interrupt breastfeeding. If there is urgency in making a diagnosis, waiting for the mother’s milk to dry up is not rational, since it may take several weeks. Even if there is a reason to stop on the side with the lump, the baby can and should continue breastfeeding on the other side.


X-rays don’t affect breast milk and a mother can continue to breastfeed straight after the X-ray3. Occasionally a contrast agent is used with an X-ray to improve the image quality of the soft tissue e.g. barium may be used, either swallowed or as an enema. As barium is chemically inactive and is not absorbed by the body, breastfeeding is not affected.4


A mammogram is another type of X-ray. Mammograms are compatible with breastfeeding but may be more difficult to interpret on a lactating breast due to the density of breast tissue 5. It is recommended that breasts are as empty as possible prior to the mammogram to maximise the quality of the images67 and that a radiographer experienced in reading images of breasts is used8.


Ultrasound helps distinguish between fluid filled (cystic) and solid masses by high frequency sound waves used to see inside the breast. Ultrasound is said to be safe to use in lactation.91011. It is recommended that breasts are as empty as possible prior to a breast ultrasound to maximise the quality of the images12

Magnetic resonance imaging (MRI)

MRI scans use strong magnetic fields and radio waves to produce clear pictures of the inside of the body. The Academy of Breastfeeding Medicine states that MRI is not contraindicated during breastfeeding:

Although MRI is less sensitive in the setting of lactation due to increased parenchymal density and vascularity, it nevertheless is not contraindicated and may provide diagnostic and treatment planning benefit.

The American College of Radiology (ACR) say:

although not the initial imaging tool of choice, screening breast MRI is not contraindicated during lactation and may be considered in lactating women with a high lifetime risk of breast cancer.

MRI with contrast: Gadolinium

About one in three MRI scans use gadopentetate dimeglumine (Gadolinium) a contrast medium to improve clarity of the images.13 Manufacturers’ package inserts may say that breastfeeding is not recommended for 24 hours after use14, however several authorities on the subject suggest this is not necessary:

  • HalesMeds online [paywall accessed October 2020] explains that Gadolinium has a short half-life (1.6 hours), is poorly absorbed orally by the mother and only reaches breast milk in incredibly low levels therefore 24 hours interruption of breastfeeding seems extreme.
  • The American College of Radiology (ACR) explains:

Because of the very small percentage of gadolinium-based contrast medium that is excreted into the breast milk and absorbed by the infant’s gut, we believe that the available data suggest that it is safe for the mother and infant to continue breast-feeding after receiving such an agent.

  • Wendy Jones, UK pharmacist and author, has reviewed the evidence and concludes MRI scans are compatible with breastfeeding with or without gadolinium and she cites guidelines from The Royal Australian and New Zealand College of Radiologists (RANZCR)1516. For more information see MRI Scans and Breastfeeding from The Breastfeeding Network.
  • Dr Jack Newman also explains:

[gadopentetate] is excreted into breast milk in extremely small amounts. Less than 0.04% of the dose administered to a mother will appear in her milk. Also, of that tiny amount excreted into the milk, only 0.8% is actually absorbed by the baby. Considering that we do MRI scans of small babies, concern about continuing breastfeeding after MRI makes no sense at all.

which is more hazardous for the baby, breast milk containing minuscule amounts of contrast media, most of which are not absorbed, or formula, even for only 24 hours? We can say unequivocally that, given the risk of interrupting breastfeeding, mothers should be reassured that they will be doing the best for their babies by not interrupting breastfeeding for even 1 second after MRI, CT, or most other radiologic procedures.

Breast biopsy

A biopsy involves taking a sample of a lump or mass within the breast. Because a biopsy may involve a surgical procedure (incision and removal of tissue) it could pose a risk to breastfeeding now or in the future due to damage to ducts, scarring and risk of infection. Core needle biopsy after a full image work-up is the preferred diagnostic procedure for a breast lump. This is due to its safety, cost effectiveness and precision. However there remains a small risk of infection, milk fistula formation, infection or bleeding1718 or a risk of developing a milk-filled cyst or galactocele19. Despite these possible complications, a biopsy is compatible with breastfeeding and stopping breastfeeding is not advocated prior to the procedure as this would lead to an increased risk of a fistula (ABM Protocol #30).

What is a milk fistula?

A fistula is an area or “hole” on the skin of the breast that constantly leaks breast milk from a milk duct below. A fistula tends to be a complication arising from a biopsy, abscess or surgical procedure on a lactating breast.20

Avoiding a milk fistula

The ABM and Dr Jack Newman says that the best way to avoid a milk fistula following a biopsy is to continue to breastfeed. Dr Newman explains:

An important factor in preventing a fistula is to continue breastfeeding on that breast. If the mother doesn’t, the milk is likely to find the path of least resistance to flow, which may be this relatively large opening [the biopsy wound]. Often a fistula becomes apparent after the sutures are taken out, so perhaps in the case of the lactating breast, sutures or staples should be left in much longer than usual. Skin glue can be used in addition to sutures or staples when closing the wound.

Should a fistula occur, it can dry up on its own without stopping breastfeeding on that side. If the mother does not want to stop breastfeeding on that side and can tolerate the leaking, there is no harm in leaving the fistula. If it is a problem, stopping breastfeeding on that breast only is an option.

Breasts work individually so if a mother decides to stop breastfeeding on the affected breast, the other side will usually compensate by increasing production. Gradually reducing the number of feeds on the breast with the fistula will give the other breast time to compensate (Newman, p 162). In this situation using medication to reduce milk supply  would affect both breasts so is best avoided. See How to Stop Breastfeeding for more information on reducing production in one breast or both.

Tests with contrast agents

Computed tomography scan (CT or CAT scan)

A CT scan uses a powerful X-ray and computer to create images from inside the body. As part of the procedure special dyes or “contrast agents” may be injected or swallowed to improve image visibility. The agents typically used are iodinated radiocontrast agents. The iodine in these agents stays bound to the molecule preventing it from entering breast milk.2122 In Computed Tomography (CT) Scans pharmacist Wendy Jones quotes the RANZCR guidelines:

Cessation of breast feeding or expression and discarding of breast milk after iodinated contrast media administration are not required

Breastfeeding after a CT scan with contrast—resources

Three useful resources discussing CT scanning and whether specific contrast media are compatible with breastfeeding are:

  • Breastfeeding and the Use of Contrast Dyes for Maternal TestsClinical Lactation, 2011, by Kay Hoover IBCLC. Comprises a comprehensive list of contrast agents and concludes that a mother can breastfeed after a CT scan with one exception—Teslascan (Mangafodipir Trisodium).
  • Computed Tomography (CT) Scans; a 2019 information sheet from The Breastfeeding Network—a breastfeeding charity in Great Britain. Discusses some named contrast media with further references.
  • Manual on Contrast Media v10.3, American College of Radiology, 2020—Chapter 19 discusses the use of iodinated or gadolinium-based contrast media in breastfeeding women. The authors conclude that such a small percentage of contrast media is excreted into breast milk and absorbed by the baby’s gut that it is safe to continue breastfeeding.

Intravenous pyelogram (IVP)

Intravenous pyelogram (IVP) is another type of X ray using a contrast medium that helps the radiologist check the health of the kidneys, ureters and the bladder. As with CT scans, iodinated compounds are used but they are not radioactive (Newman, 2007).

Breastfeeding and cancer screening

The American College of Radiology (ACR) document Breast Imaging of Pregnant and Lactating Women provides up-to-date information on diagnostic techniques for breast imaging during lactation and pregnancy.23

In Cancer and Breastfeeding (Breastfeeding Today, LLLI, 2015), Diana West, IBCLC answers the most commonly asked questions breastfeeding mothers have when faced with testing and treatment for cancer including; imaging techniques, needle aspiration, biopsy, radioactive isotopes, radiation therapy, chemotherapy and anaesthesia. West explains:

Imaging techniques used for diagnosis of pathology (such as ultrasound, mammogram, magnetic resonance imaging (MRI), positron emission tomography (PET) scan, 2-Methoxy Isobutyl Isonitrile (MIBI) scan, electrical impedance tomography (EIT) scan, computed tomography (CT) scan/computer axial tomography (CAT) scan, thermography, or diaphanography) are non-invasive and do not affect milk production or safety. It may be more difficult to interpret breast tissue results due to the increased density from lactation, but it is not impossible. It is not necessary to interrupt or suspend breastfeeding to have these procedures.

Breastfeeding during chemotherapy is absolutely contraindicated because the medications used to eradicate cancer are highly toxic and transfer into milk. Breastfeeding after chemotherapy has been completed may be possible, either by relactation or as a result of another pregnancy, depending upon the drugs that were used.

Breast cancer mutation and screening

A useful paper by Carmichael et al24 discusses breast cancer screening in women who have breast cancer mutations and are pregnant or breastfeeding. Their summary includes:

  • Encourage all women to breastfeed as it can reduce their risk of breast cancer and has many health benefits for the breastfed baby
  • Recommend breast awareness and a clinical breast examination every six months in women with BRCA (breast cancer) mutations who are breastfeeding
  • If a woman has never had breast screening or is outside the recommended interval between screenings, recommend she have a breast MRI if she intends to continue breastfeeding.

Mother sits on bench with toddler


Can I breastfeed after radioisotopes?

Some medical diagnostic tests require radiopharmaceuticals (radioactive drugs that use different radioisotopes) e.g. a lung VQ scan, renal, marrow or bone scan. Radioisotopes may require stopping breastfeeding for a short time to avoid exposing a baby to excess radioactive material. The period of interruption will depend on the type of radioactive substance used, and the dosage and age of your baby. The mother will need to pump regularly during any interval to avoid mastitis or a drop in her milk supply. If a mother has sufficient expressed breast milk already stored prior to the test, this can be fed to her baby during this waiting period. See below for information on whether the milk pumped during the break in breastfeeding can be used after a waiting time or whether it should be thrown away.

Iodine 131 treatment

If radioactive iodine I-131 treatment is required (e.g. for thyroid cancer or hyperthyroidism) breastfeeding mothers are advised to stop breastfeeding and wean before treatment. Iodine-131 concentrates in the thyroid gland as well as breast milk and breast tissue. Exposing a baby to this breast milk could affect their own thyroid gland function or future risk of thyroid cancer and increase the mother’s radiation exposure in the breast tissue.25

VQ Scans and breastfeeding

A lung scan or ventilation-perfusion (VQ) scan is a diagnostic test that uses radiopharmaceuticals to check for a blood clot in the lungs (pulmonary embolism).26 Inside Radiology recommends interrupting breastfeeding for 24 hours after this type of scan:

If you are breast-feeding, it is advised that you stop breast-feeding for the 24 hours after the scan. This is so that your baby is not unnecessarily exposed to radiation. During this time, your milk can be expressed, but it need not be discarded. It can be stored in the fridge and can be used to feed your baby 24 hours after the VQ scan.

Whether 24 hours is required in all cases may depend on the radioisotope used during the test and the protocols in place at individual hospitals. See below for further information and resources to refer to.

Radioisotopes for a breastfeeding mother

Following a diagnostic test with a radioisotope on a breastfeeding mother, the radioactivity of the mother’s expressed breast milk will gradually dissipate during storage. How long breast milk will need to be stored will depend on the precise product that has been used and it’s half-life (the time needed for the amount of the drug in the body to be reduced by half). In Use of Radioisotopes (and Other Imaging Agents) During Lactation Kelly Bonyata explains that as a general rule breast milk stored in the waiting period after a diagnostic test with a radioisotope can be used after five half lives have passed:

You do not need to dump this milk. It can be dated, frozen and used after 5+ half-lives of the radioisotope have passed (after 5 half-lives, 96.9% of the radiation is gone; after 10 half-lives, 99.9% of the radiation is gone). You may also get your milk checked for radiation by your radiology/nuclear medicine department.

Technetium 99M

In Breastfeeding and Radioactivity, iLactation online conference 2013, Veronica Garea, Head of the Department of Safety and Environmental Impact (INVAP), stated that the preferred radioisotope for a breastfeeding mother is Technetium 99 metastable (Tc99m).

Jack Newman explains how long technetium remains in the body:

Technetium has a half-life (the length of time it takes for ½ of all the drug to leave the body) of 6 hours, which means that after 5 half-lives it will be gone from the breastfeeding parent’s body (do the math). Thus, 30 hours after injection, all of it will be gone (well 98% will be gone) and the breastfeeding parent can breastfeed the baby without concern about the baby getting radiation. But does all the radioactivity need be gone? After 12 hours, 75% of the technetium is gone, and the concentration in the milk very low. I think that waiting 2 half-lives is enough, for a material such as technetium. But: Not all technetium scans require stopping breastfeeding at all (HIDA scan, for example).  It depends on which molecule the technetium is attached to. discuss that although the radioactive half-life of Tc-99m is fixed at six hours the time needed to stop breastfeeding or store breast milk may be less than 30 hours (five half lives) as it will depend on which formulation of Tc-99m is used and recommendations can also vary between advisory bodies. Hale lists formulations that require cessation of breastfeeding for four hours and others where breastfeeding should be interrupted for 12–24 hours. However, for those who prefer a conservative approach, Hale recommends storing breast milk for 30 hours post procedure after which time the stored milk will be safe to use.27

Precautions for breastfeeding and physical contact after radioisotopes

Inside radiology describes the precautions following radioisotopes:

  1. Interrupt breastfeeding as directed by the medical team to give time for the radioactivity to reduce to an acceptable level. Any breast milk pumped during this period can be stored in the fridge or freezer for use after the restriction period.28
  2. Minimise close contact with children after the procedure for the same specified period of time as in #1 above, keeping a distance of 2-3 metres between parent and child where possible (Cain, 2018) taking account of the children’s emotional needs:

it is important to remember the emotional needs of the child. If the child needs a cuddle then this should occur. The child can be touched or kissed, but if another carer is available to comfort the child, then this would be preferable. If the child is happy and/or content, then a safe distance of 2–3 metres should be maintained between the child and the person who received the radiopharmaceutical.

Good resources for looking up compatibility of radioactive materials in medical tests while breastfeeding, and how long breastfeeding should be interrupted include:


Many medical tests are compatible with lactation and do not require breastfeeding to be interrupted. X-rays, MRIs, CT scans, Intravenous Pyelogram (IVP), ultrasound and mammograms do not affect breast milk. Radioisotopes however, may require interrupting breastfeeding for a short time to avoid exposing a baby to excess radioactive material. Information for best practice for different radioisotopes is available online to discuss with your health professionals.

This article should not be construed as medical advice. Always check with your medical professional for the latest guidance on compatibility of medical procedures with breastfeeding.

**Excerpts reproduced by permission of Pinter and Martin.