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Cancer during pregnancy

Cancer during pregnancy is rare. Because it’s rare, not a lot of research has been done. We expect that the number of women diagnosed with cancer while pregnant will increase because more women are waiting until they are older to have children and the risk of developing most cancers increases with age.

Because there is not a lot of information available about cancer during pregnancy, making decisions that are right for you can be hard. There are many issues to consider.

You may worry that cancer or its treatment will affect your well-being and the well-being of the baby. You may also worry about the effect of tests to diagnose cancer on the well-being of your baby.

Some cancer treatments are safe for the fetus during pregnancy or only during certain times of pregnancy. Others are not safe for the fetus at any time. Most cancers do not spread from a woman to the fetus even though some may spread to the placenta. Recent improvements in treatments and careful monitoring provide safer conditions for pregnant women with cancer so that it is more likely that the baby will be successfully delivered with good outcomes. It is important to know that a pregnant woman with cancer can give birth to a healthy baby.

Types of cancer

Pregnancy itself does not cause cancer, and pregnant women do not have an increased risk of developing cancer compared to women who are not pregnant.

Some of the most common cancers diagnosed during pregnancy include:

  • breast (the most common)
  • cervical
  • Hodgkin lymphoma
  • non-Hodgkin lymphoma
  • ovarian
  • malignant melanoma
  • leukemia
  • thyroid
  • colorectal

Other types of cancer such as brain, bone and lung can occur when a woman is pregnant, but they are very rare.

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Diagnosing cancer during pregnancy

Many symptoms such as nausea, vomiting, abdominal bloating, rectal bleeding, fatigue and headaches are common during pregnancy. Occasionally, these symptoms can also be related to a particular type of cancer. It is important to talk with your doctor about symptoms if they continue or happen at a time during the pregnancy when it is no longer considered typical.

Sometimes pregnancy can uncover cancer earlier than it would otherwise have been found. For example, a Pap test done as part of routine care during pregnancy can find cervical cancer. An ultrasound done during pregnancy may find ovarian cancer at an early stage.

If cancer is suspected, women and their doctors are often concerned about using tests to diagnose cancer because of potential harm to the fetus. For example, you may be worried about the radioactivity in tests such as x-rays, CT scans or nuclear medicine tests. But some of these tests can be used safely during pregnancy, giving your doctor extra information to best manage your cancer.

  • Research has shown that the level of radiation in an x-ray (with appropriate shielding) used to diagnose cancer is too low to harm the fetus.
  • CT scans use a higher level of radiation than routine x-rays and are much more accurate at showing internal organs and structures. They can be very helpful in making a diagnosis of cancer or the spread of cancer. But CT scans of the abdomen or pelvis should only be done if absolutely necessary to plan for your cancer therapy.
  • Whether these tests cause harm to the fetus depends on the stage of pregnancy, the number and type of x-rays used, the amount of radiation used and if the fetus is shielded from the radiation. A lead shield is always used to cover the mother’s abdomen for extra protection during both x-rays and CT scans.

MRIs and ultrasounds are considered safe during pregnancy because they do not use radiation. Physical exams and many biopsies are also safe and important tools to diagnose cancer.

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Cancer treatment during pregnancy

Treating cancer during pregnancy is very complex. Many people think that having treatment for cancer will always harm the mother or the baby. In the past, the doctor often recommended not to continue with (to terminate) the pregnancy because of this concern.

Before being treated for cancer and throughout your pregnancy, your obstetrician will assess the age of the fetus, maturity of the fetus and expected delivery date to help plan your treatment and ensure the baby is growing properly.

The healthcare team will look at the best treatment options for the mother, balancing this with possible risks to the fetus. The treatment options for a pregnant woman with cancer are the same as those of the non-pregnant woman with cancer, but how and when the treatment is given may need to be changed.

The type of treatment and when it may be given depends on many factors:

  • the location of the cancer
  • the type of cancer
  • the stage of the cancer
  • how old the fetus is (how long the woman has been pregnant)
  • the wishes of the mother

Treatment is tailored to each woman. Cancer treatments used during pregnancy may include surgery, chemotherapy and sometimes radiation therapy, but these are only used after careful thought and planning to ensure the safety of both the mother and the baby.

Some cancer treatments can harm a fetus, especially during the first 3 months of pregnancy, called the first trimester. This is when the baby develops its body structure and organs. Sometimes cancer treatment may be delayed until later in the pregnancy, during the second or third trimester.

When cancer is diagnosed later in a pregnancy, sometimes it may be possible to wait to start treatment until after the baby is born. The doctor may also consider inducing, or bringing on, labour early.

For some very early stage cancers, such as very early stage cervical cancer, it may be safe to continue the pregnancy to term and delay treatment until after the baby is born.

In some situations, the woman, and the doctor need to discuss whether or not to continue with the pregnancy. Providing treatment right away may be the safest option for some women with more advanced or aggressive cancers found early in a pregnancy.

Surgery

Generally, surgery poses the least risk to the fetus and may be considered the safest cancer treatment option for some cancers, especially after the first trimester. Improvements in surgery and anesthetics, and careful monitoring of the mother and baby, make it possible to lessen the risks to both mother and baby.

Chemotherapy and other drug therapies

Chemotherapy is the use of anticancer drugs to treat cancer. It is a systemic therapy. This means that the drug travels throughout the body and destroys cancer cells. Chemotherapy and other drugs used to treat cancer are toxic and have the potential to harm a fetus, especially if they are given during the first trimester of pregnancy, when the organs of the fetus are developing.

Chemotherapy during the first trimester can cause birth defects and low birth weights or may cause a woman to miscarry. The risk of birth defects when chemotherapy is given during the first trimester varies according to the chemotherapy used.

Some effects of chemotherapy and other drug therapies on a fetus are not known, especially for newer drugs like biological therapies or targeted therapies.

Because there has not been much long-term follow-up of children exposed to chemotherapy in the uterus, there is not a lot of information about long-term effects on, for example, thinking ability and brain and behaviour development. One recent study followed children up to 18.5 years of age who had been exposed to chemotherapy in the uterus during the first trimester of pregnancy. It showed that the children were still fertile (they will be able to conceive or produce children of their own) and no nerve or psychological problems were found.

Some chemotherapy and other drugs may be given during the second and third trimesters without causing harm to the fetus. Protection is provided by the placenta. The placenta develops during pregnancy and connects the blood supplies of the mother and baby. It provides nutrients and removes waste products. It also acts as a barrier between the mother and the fetus that many chemotherapy drugs cannot pass through. But chemotherapy given during the second and third trimesters is associated with early labour and low birth weight.

Chemotherapy and other drug therapies can also cause health problems in the woman such as infection, anemia or nausea and vomiting. These problems can indirectly harm a fetus.

Radiation therapy

Radiation therapy uses high-energy x-rays or particles to destroy cancer cells and shrink tumours. Radiation can harm a fetus, especially during the first trimester when the baby’s organs and nervous system are developing, so radiation treatment is usually not recommended during this time. Whether or not radiation therapy can be used in the second or third trimester depends on the dose of radiation and the area of the body being treated.

When radiation therapy is possible, careful planning is used when treating pregnant women with cancers that are far away from the pelvis (such as breast cancer or head and neck cancers). Lead shields or blocks are used to reduce as much as possible the amount of radiation the fetus is exposed to. Radiation therapy for breast cancer can usually be delayed until after the baby is born.

Cancers in the pelvis in a pregnant woman cannot be treated effectively with radiation therapy without causing severe problems for the fetus. In this case, for a woman who is between 1 and 26 weeks pregnant, the doctor will often recommend not to continue with the pregnancy. And radiation is usually not recommended regardless of the stage of pregnancy. Possible effects on the fetus during this time include malformation of the organs, small brain, mental retardation, developmental delays, stunted growth and other growth abnormalities.

The International Commission on Radiological Protection has developed guidelines for safe radiation exposure during pregnancy. If the fetus is exposed to more than this amount, the doctor will recommend that the pregnancy be terminated.

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Prognosis

The prognosis for a pregnant woman with cancer is often the same as for women of the same age with the same type and stage of cancer. In general, most cancers do not negatively affect a pregnancy, and pregnancy does not affect the cancer outcome. But the treatments for cancer may have a harmful effect on the fetus. If a cancer diagnosis is not found early because of pregnancy, these women may have a poorer overall prognosis than women who are not pregnant and are diagnosed earlier.

Pregnancy may affect the behaviour of some cancers. For example, hormone changes that occur during pregnancy may stimulate some cancers, such as malignant melanoma, to grow.

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Effect of cancer on the fetus

The effects of cancer on the fetus are still largely unknown, but it seems that cancer only rarely has a direct effect on the fetus. Only a few cancers can spread from the mother to the fetus. These include malignant melanoma, small cell lung cancer, non-Hodgkin lymphoma and leukemia.

If the cancer has not spread to the newborn, then no preventive, or prophylactic, treatment will be given to the baby. But the healthcare team will closely monitor the baby and watch for early signs of cancer if there’s a chance that it may spread from the mother.

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Breastfeeding

Cancer cells cannot pass to the infant through breast milk. But chemotherapy and other drugs can be transferred to the baby, and this can cause harm. Also, radioactive substances that are taken as a drink or a pill (such as radioactive iodine used to treat thyroid cancer) can also get into the breast milk and harm the baby. So women being treated for cancer are often advised not to breastfeed.

Always ask the healthcare team if it is safe to breastfeed.

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