What Happens to the Immune System During Pregnancy?

Immune System Pregnancy

You might have gathered by now that your immune system is somehow different when you’re pregnant. You might have heard on the news that babies, the elderly, and pregnant women are more susceptible to certain infections. Or you may have been asked about getting the flu shot or other vaccinations. Additionally, you probably know that certain foods should be avoided during pregnancy to prevent certain infections. But why? We’ll get into that below, but first, let’s review the basics of the immune system.

What is the immune system?

The immune system is what keeps you healthy. It protects the body from “foreign pathogens,” or things outside the body that may cause harm, such as bacteria, viruses, and other diseases. This system is made up of the following:

  • different types of white blood cells (e.g., natural killer cells, regulatory T cells)
  • bone marrow
  • the spleen
  • the thymus
  • lymph nodes
  • lymph vessels

It’s the job of the immune system to recognize those pathogens and attack them in order to keep infections and diseases at bay.

Why is it different in pregnancy?

After learning about how the immune system works, you can imagine that when a fetus begins to grow inside you, it may be recognized as “foreign.” The immune system has to change so mother and baby can coexist without a problem. While some of the changes are understood, exactly why the mother’s body does not reject or attack the fetus is still a bit of a puzzle. It is often said that the immune system is “suppressed” during pregnancy. However, scientific research suggests that’s not completely accurate. In fact, infection and the immune system’s response can lead to preterm labor. It is thought that this may be the body’s way of protecting itself and its species, but it’s not clear why it happens only sometimes.

All these things considered, there must be a balance between 1) allowing the fetus to develop without rejection and 2) protecting against illness and infection. Therefore, it’s probably more appropriate to say that the immune system undergoes adaptation or modification during pregnancy, rather than suppression. In other words, the immune system changes but does not weaken during pregnancy.

Another interesting aspect of this has just been discovered. Recently, researchers at Stanford found that the immune system changes in pregnant women follow a time schedule, or what they’re calling an “immune clock.”3 This information is exciting because it may help scientists better understand certain aspects of immune changes in pregnancy, especially prenatal infections and preterm labor.

Enough with the science – what does this mean for me?

When you’re pregnant, it’s important to be aware of these changes in order to avoid illness. It’s also important to stay up to date with the vaccinations your obstetrician recommends. This is not only because your own immune system has changed, but also because you are protecting your growing baby, who depends on you to keep her safe and healthy.

To help you understand why this is important, it’s helpful to know how vaccines work. Vaccines are made of weak or inactive cells that would usually make you sick. They are designed to “look” like the infection, so they prompt the immune system to attack them. Once the body knows how to attack this “infection,” it will remember it in the future if you’re exposed to it again. Basically, vaccines help the immune system fight infections better.

In addition to getting vaccinated, there are other ways for pregnant women to try to prevent illness. This includes avoiding certain foods, limiting exposure to people who are sick, and practicing good hand hygiene. Washing your hands regularly is one of the best and easiest ways to keep from getting sick.

Special populations

Autoimmune diseases occur when the body’s immune system mistakenly sees itself as foreign and attacks parts of the body, such as the immune system. Women with autoimmune disease, such as multiple sclerosis (MS) or inflammatory bowel disease (IBD), may experience changes in their conditions during pregnancy. For example, patients with MS commonly report that their symptoms improve dramatically during pregnancy, and some report that their symptoms worsen after pregnancy. If you have an autoimmune disease, it’s important to speak with your doctor(s) about how pregnancy might affect your condition.

Mandy Armitage
Dr. Mandy Armitage is a board-certified physician and writer. She is passionate about education, for patients and clinicians alike. In her free time, she enjoys spending time with her family, reading, traveling, and attending live music events.

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