Is Treatment Safe for Your Baby?

Even if you've been reassured that getting pregnant after a breast cancer diagnosis is safe for you, you're probably still worried about how the cancer and treatments might affect your baby.

If breast cancer is in your body during pregnancy, can it spread to the baby?

No. A barrier between the mother's and the baby's body blocks any cancer cells from entering the baby or its blood supply.

Will hormonal therapy cause birth defects?

Tamoxifen is considered unsafe to take during pregnancy. So if you're trying to get pregnant, or you think you might be pregnant, you should not be taking tamoxifen. Work with your doctor to figure out how long you can be on tamoxifen to get the most critical benefit while not losing the opportunity to get pregnant. Read more on our page Tamoxifen and Fertility

Will chemotherapy during pregnancy cause birth defects?

Depending on the stage of the cancer, some pregnant women with breast cancer may need chemotherapy. Doctors do not generally give women chemotherapy during the first trimester (first three months) of pregnancy because it could harm the organs of the fetus that are developing during that time.

A women diagnosed with breast cancer during her first trimester may opt to delay starting chemotherapy until she starts her second trimester. But one small study suggested that a chemotherapy treatment delay of 3 to 6 months could increase the risk of the cancer spreading outside the breast by 5% to 10%. Whether or not you decide to delay treatment depends on the type of cancer you have, how urgently your doctor thinks you need to begin chemotherapy, and how important it is for you to continue your pregnancy.

Several studies have shown that FAC chemotherapy (fluorouracil, Adriamycin, and cyclophosphamide) given during the second or third trimesters of pregnancy is surprisingly safe. Rarely does such treatment appear to cause miscarriages, premature birth, stillborns, or birth defects. Remember, though, that this combination might have a negative effect on your future fertility—your ability to get pregnant again after treatment is over. The types of chemotherapy that are considered safe during pregnancy (see below) may not be the same as those that have a low risk of affecting your fertility in the future. (See Will Chemotherapy Make You Infertile?)

Also, few studies have followed, for long periods of time, the children born to women who received chemotherapy for breast cancer during pregnancy. One study that did so found no obvious abnormalities in the women's children, aged 15 to 20 years.

Some types of chemotherapy are thought to be safer for a developing baby than others:

• Methotrexate is probably the riskiest. It is known to cause miscarriages and possible birth defects.
• There is contradictory evidence about whether fluorouracil, or 5-FU, is especially harmful to the fetus. One study found it caused no problems when given during the second and third trimester of pregnancy, while another found it to be as damaging as methotrexate.
• Vincristine, Velban (chemical name: vinblastine), and Adriamycin (chemical name: doxorubicin) are thought to be some of the safest chemotherapy drugs to take during pregnancy. These medicines may even pose low risk of harming the baby when given during the first trimester of pregnancy.
• Cytoxan (chemical name: cyclophosphamide) is thought to be moderately risky when taken during the first trimester, and relatively safe when it is given during the last two trimesters of pregnancy.
• Few studies have looked at the effect of taxanes such as Taxol (chemical name: paclitaxel) or Taxotere (chemical name docetaxel) on the developing fetus. So it's unclear if these drugs can also be safely given during the second and third trimesters of pregnancy. One researcher reported giving a taxane to a woman in her third trimester of pregnancy. The woman gave birth to a normal baby.

Chemotherapy can lower immune cell count

Chemotherapy can reduce the number of infection-fighting white blood cells in your body. This side effect can happen to you and to the fetus with chemotherapy during pregnancy. It does not usually pose problems for the fetus. But if low levels of white blood cells persist after birth, it can be dangerous for both the mother and the infant.

If possible, women should not get chemotherapy about a month before delivery to avoid it causing low levels of white blood cells for them or their babies at birth. A French study found that of 17 women who had chemotherapy for breast cancer within a month before delivery, one had a newborn with low white blood cell counts.