Feature Article: Infectious Diseases and Pregnancy

Pregnancy is a time of hope, anticipation—and many questions. Because pregnant women have to consider not only how their actions and exposures will affect them but also their unborn babies, infections and vaccinations, in particular, can be a source of concern. Indeed when it comes to questions related to immunity and health, a mom-to-be should understand how intricately her and her unborn child’s immune systems are entwined.

Immunity: The Basics

When women are pregnant, their bodies undergo many changes, including changes to their immune system. A pregnant woman’s immune system needs to allow for a “foreign tissue” to grow inside of her without seeing it as foreign and making an immune response against it. Because the pregnant woman’s immune system is somewhat suppressed (in an effort to avoid making an immune response directed against the baby), a woman may be more susceptible to infections that might otherwise be more easily handled.

In addition to the immune system changes, pregnant women undergo physical changes that make them more susceptible to infections. For example, their heart and lungs need to work harder as they accumulate more fluid. This sets the stage for complications that might otherwise be uncommon for healthy, non-pregnant women of the same age. For example, pregnant women are seven times more likely to suffer a severe bout with influenza than women of the same age who aren’t pregnant.

Women’s immune systems also protect the unborn baby since blood (and, therefore, the immune cells that travel in blood) also circulates in the baby. And, when the baby is born, antibodies introduced through the placenta and breast milk, called maternal antibodies, are responsible for keeping the baby healthy while the baby’s own immune system begins generating an immune response to all of the natural challenges in the environment.

For these reasons, vaccinations, and their timing, become particularly important.

Are there vaccines I need before becoming pregnant? 

If you are thinking about pregnancy, you should check that you are up to date on all of your vaccinations, particularly those that are live weakened viral vaccines, such as the measles-mumps-rubella (MMR) and chickenpox vaccines. These recommendations are important for two reasons. First, these four viruses can be particularly harmful to developing fetuses. Women infected with measles, mumps, rubella or chickenpox during pregnancy can have babies with defects resulting from the infection. Second, although the risk is theoretical at best, the fact that the vaccine viruses replicate have led officials to recommend against giving these vaccines during pregnancy if it can be helped. During an outbreak, pregnant women may be advised to get vaccinated because the risk to the baby if the woman is infected is greater than the risk of being vaccinated. However, if women ensure they are immunized before becoming pregnant, this situation will never be realized.

Are there vaccines I should avoid if I am pregnant?

Yes. Although vaccines given during pregnancy have not been found to cause harm to unborn babies, theoretical concerns related to live viral vaccines have led officials to recommend against giving them during pregnancy unless the risk of infection is imminent. To this end, MMR, chickenpox and the intranasal influenza vaccine should be avoided, if possible.

However, it is important to be aware that when these vaccines have been given to pregnant women, inadvertently, such as before a woman knew she was pregnant, or because of a known risk of infection, no harm has been done.

On the other hand, pregnant women infected with some of these natural viruses have suffered increased complications or hospitalizations, miscarriages, premature labor or harm to the unborn child.

Why should I get an influenza vaccine during pregnancy?

Influenza virus infects tissues of the lungs. Because of the physical changes to a woman’s body when she is pregnant, such as increased fluid retention and the increased effort required of the lungs, a pregnant woman is more likely to experience complications that require hospitalization, such as pneumonia, if infected with influenza virus. Women who get the flu are also at increased risk for preterm labor.

Since babies cannot get the influenza vaccine until 6 months of age, options for protecting them against influenza are limited to controlling exposure and leveraging maternal antibodies. Since people can transmit influenza before the onset of symptoms, controlling exposure may not always be possible. Therefore, maternal antibodies offer an extra level of assurance. Indeed, studies have shown that during influenza season, babies born to women who were immunized against influenza are less likely to become ill from influenza when compared with babies born to women who were not.

Why should I get a Tdap vaccine at a certain time during pregnancy?

Pregnant women are recommended to receive a single dose of Tdap vaccine between 27 and 36 weeks of gestation during each pregnancy. The main reason for this vaccination is to protect unborn babies from getting pertussis in the weeks and months after birth before they are protected by the first three doses of the DTaP vaccine, typically given at 2 months, 4 months and 6 months of age.

Pertussis is a bacterial infection that is particularly dangerous for young infants. The infection causes severe coughing spasms that preclude babies from moving air through their small windpipes. Babies in the midst of a coughing spasm caused by pertussis often make a “whooping” sound as they struggle to breathe and sometimes, if the spasm lasts long enough, they turn blue. In addition to being quite scary for parents to watch, these spasms can be harmful and, sadly, are sometimes fatal.

Because young infants cannot get the DTaP vaccine and often require several doses to be protected, the best ways to protect them are to control exposure or leverage maternal antibodies. Studies have shown that most babies get pertussis from their moms or siblings who have a cough, making controlling exposure next to impossible. Efforts to control exposure by making sure everyone around the baby has received a Tdap vaccine (known as cocooning) may help, but are not foolproof. Therefore, boosting maternal antibodies that will be transferred to the baby through the placenta and in breast milk provides an added measure of protection.

The recommended timing to receive the Tdap vaccine during pregnancy allows for the most robust maternal antibody response right before the birth of the baby, affording the baby the best opportunity to be protected.

If I am pregnant and have a young child in the home, are there any vaccines that my child can’t get while I am pregnant?

No. Others in the home of a pregnant woman, both children and adults, can receive any vaccines they may require without fear of harm to the pregnant woman or her unborn child.

If I am going to breastfeed, do I need to avoid certain vaccines?

No. Breastfeeding women can get any vaccines they may need without fear of harm to the baby.

If I am breastfeeding, are there vaccines I should delay for my baby?

No, infants who are being breastfed can get vaccines according to the recommended immunization schedule. In fact, the recommended schedule is designed to ensure that babies have generated their own antibodies before maternal antibodies wane to a point that they are no longer protective

This information is available in an easy-to-print PDF. The sheet can also be photocopied for sharing with others.