Overview

Your gut does much more than digest food, it is a key player in your immune system, mood regulation, and overall health, especially during pregnancy. Your gut microbiome consists of trillions of bacteria, both good and bad. Maintaining a healthy balance between them is key to keeping everything functioning properly. Hear about the research on how your gut microbiome can affect common pregnancy symptoms like constipation and risks for complications like GBS and preeclampsia. Learn about the evidence on how to support a healthy gut microbiome during pregnancy and beyond, from including probiotic-rich foods in your diet to selecting a high-quality probiotic supplement.

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The Gut

The gut is a simple name for the very complex gastrointestinal system, also known as the digestive system or digestive tract. This includes the mouth, esophagus, stomach, pancreas, liver, gallbladder, small intestine, colon, and rectum.

The moment food enters your mouth, digestion begins. Chewing breaks it down, and saliva starts the digestive process. After you swallow, food moves down your esophagus and into your stomach, where it is further broken down by acids and enzymes.

Your pancreas produces enzymes to break down proteins, fats, and carbohydrates. Your gallbladder stores and releases bile into the small intestine to aid fat digestion. The small intestine breaks food down into amino acids, sugars, and fatty acids that you absorb into your bloodstream. Blood from your digestive system flows to the liver, where your liver filters it to remove toxins, metabolize drugs, store nutrients, and create proteins and bile.

What remains then moves to the colon, or large intestine, to extract salt and water. Bacteria in the colon ferment any leftover sugars, starches, and proteins, converting them into short-chain fatty acids that your body can use for energy. Finally, the waste products go to the rectum and you eliminate it from the body.

The Gut Microbiome

Your gut microbiome consists of trillions of bacteria, both good and bad. Maintaining a healthy balance between them is key to keeping everything functioning properly. Ideally, about 85% of the bacteria in your gut should be beneficial, with the remaining 15% made up of less helpful or potentially harmful types.

For simplicity, this article will focus on how bacteria function within your gut, but it’s important to remember that this is a highly complex system that plays a much larger role in your overall health than just digestion.

The Gut-Immune Connection

Your gut does much more than digest food. It plays a major role in your overall health. Around 70% of your immune system is located in your gut. For these immune cells to function properly, it’s essential to maintain a healthy gut microbiome. This is especially important during pregnancy, when your immune system is naturally suppressed. There is evidence that probiotics can support immune function by interacting with gut cells and triggering signals that enhance protective immune responses without causing inflammation. Healthy bacteria help strengthen the gut lining, boost beneficial immune cells like T cells and antibodies, and promote a balanced microbiome by keeping harmful bacteria in check. Bifidobacterium is a strain shown to interact with immune cells and influence key pathways in innate and adaptive immune systems.

The Gut-Brain Axis

The gut is closely connected to the neurological system through what’s known as the gut-brain axis. This is a two-way communication network between your gastrointestinal tract and your brain. One of the main components of this connection is the vagus nerve, which runs from the brainstem to the abdomen and carries about 90% of its signals from the gut to the brain. Another key player is the enteric nervous system, often called the “second brain,” which comprises around 100 million nerve cells embedded in the walls of the digestive tract. While it can function independently, it constantly sends and receives signals from the brain.

Your gut also produces many of the same neurotransmitters as your brain. You produce around 90% of serotonin and 50% of dopamine in the gut. These both play major roles in mood and emotional well-being. The bacteria that make up your gut microbiome can influence these neurotransmitters and affect brain function by producing signaling molecules, reducing inflammation, and interacting with the immune system. Hormones and immune system messengers also play a role in gut-brain communication, helping regulate everything from mood and stress to cognitive function. Your gut health is closely tied to your mental and emotional health.

What is a Probiotic?

A probiotic is a food or supplement containing beneficial microorganisms, such as bacteria or yeast, often called “good” bacteria. Many probiotic supplements include multiple species, called broad-spectrum or multi-strain probiotics. You may also have heard the term prebiotic, which refers to types of dietary fiber that feed the good bacteria already living in your gut. A product containing both prebiotics and probiotics, is a synbiotic.

Before probiotics were available in supplement form, people regularly consumed them through their diets. Natural sources of probiotics include fermented foods like sauerkraut, kimchi, yogurt, kefir, kombucha, and tempeh.

Why Probiotic-Rich Foods Matter

Today, most people eat fewer fermented foods and are regularly exposed to things that can influence or harm the good bacteria in their guts. Hormonal fluctuations, like those you experience during pregnancy, can also influence the gut microbiome.

Many factors can disrupt the balance of good bacteria in your gut. Processed foods often contain preservatives, artificial sweeteners, and additives that can negatively impact gut health. Excessive alcohol consumption can damage the gut lining and alter bacterial balance, and tobacco use has been shown to reduce microbial diversity and promote the growth of harmful bacteria.

Environmental factors also play a role. Overuse of antibacterial products like soaps, sanitizers, and cleaning supplies can lower your exposure to beneficial microbes. Toxins from pesticides, heavy metals, and other pollutants may also negatively affect the gut microbiome.

Lifestyle habits like poor or inconsistent sleep and chronic inflammation can disrupt the gut environment, making it harder for beneficial bacteria to thrive. Even birth and early feeding choices can influence gut health. Babies born by cesarean or fed formula instead of breast milk tend to have different, and sometimes less diverse, gut bacteria, which can affect long-term health.

Antibiotics, while important for treating infections, kill harmful and beneficial bacteria in your gut. After a course of antibiotics, it can take weeks or even months for your gut microbiome to fully recover.

To support a healthy gut, focus on two things. First, prioritize habits and foods that help good bacteria thrive. Second, reduce or eliminate the factors that can harm your gut microbiome.

Probiotic-Rich Foods

The first line of defense to support your gut health is to regularly include probiotic-rich foods and fiber in your diet. Foods that are good sources of probiotics include:

• Yogurt (Look for “live and active cultures” on the label and opt for plain or low-sugar varieties)
• Kefir (fermented milk or coconut milk)
• Sauerkraut and Kimchi (fermented vegetables)
• Natto (fermented soybeans)
• Kvass (fermented beet beverage)
• Miso (fermented soybeans/rice/barley, usually in soup)
• Kombucha (fermented tea)

During pregnancy you should be mindful of some foods. Kombucha may contain trace caffeine or alcohol. Raw dairy is generally advised against due to the risk of harmful bacteria like listeria.

High-Fiber Foods

Fiber feeds the good bacteria in your gut, helping them thrive, and the byproducts they create support your gut lining, reduce inflammation, and keep your entire digestive system healthy. Plus, fiber-rich foods may help with constipation, a common pregnancy symptom. Fresh fruits and vegetables are a good source of fiber. Juices from fruits or vegetables do not contain nearly the amount of fiber, so you want to be sure you are eating whole fruits and veggies. Other foods high in fiber include beans, nuts, seeds, and whole grains. Whole grains include brown rice, barley, buckwheat, bulgur, millet, oatmeal, quinoa, and rolled oats.

Probiotics and Pregnancy

We have covered the importance of maintaining a healthy gut and getting probiotics from your diet, and this information applies to everyone. Probiotics can be especially helpful during your pregnancy, in the postpartum period, and when breastfeeding.

A recent review of probiotics during pregnancy found that supplementation with Lactobacilli alone or Lactobacilli with Bifidobacterium seems protective. Probiotics may improve insulin resistance and reduce the risk of gestational diabetes. Researchers found probiotics may influence brain activity to reduce anxiety and depression. Probiotics are found to make vaginal flora friendlier to beneficial bacteria and enhance anti-inflammatory or reduce pro-inflammatory cytokines. Researchers also found probiotics may decrease eczema in breastfed infants and prevent allergic reactions.

Constipation

In addition to overall health, probiotics can also impact some common pregnancy symptoms. Constipation is difficult or infrequent bowel movements, hard stools, and stomach pain or discomfort. Unfortunately, this is a common symptom during pregnancy and affects 40% of pregnant women and 52% of women postpartum. Several changes in pregnancy can cause constipation. Increased progesterone levels relax the smooth muscles in your digestive tract, which slows digestion. This gives your body more time to absorb nutrients but also can contribute to constipation. Increased levels of iron from your prenatal vitamin can also make you constipated. Later in your pregnancy, as your uterus grows, it can pressure your digestive tract and rectum, leading to constipation.

There is evidence that probiotics can positively impact bowel movements for people experiencing constipation. A triple-blind randomized controlled trial evaluated the effect of consuming yogurt enriched with Bifidobacterium and Lactobacillus on the symptoms of constipated pregnant women. From weeks 24-28 of pregnancy, participants consumed 300g (about 10.5 ounces) of yogurt three times per day. One group had conventional yogurt; the other had yogurt enriched with additional probiotics (Lactobacillus acidophilus and Bifidobacterium lactic).

They found symptoms significantly improved in both groups. 300g/10.5 ounces of yogurt three times per day is a lot and is not likely realistic for most expecting moms. The takeaway is that yogurt can positively affect symptoms of constipation. Another study that used probiotic supplementation rather than yogurt found probiotics (primarily Lactobacillus) significantly reduced the severity of nausea, vomiting, and constipation and improved life quality.

See this episode for the evidence on interventions to relieve constipation during pregnancy, ranging from diet and lifestyle changes to supplements and over-the-counter medications.

Group B Strep

Group B strep (GBS), short for group B streptococcus, is a type of bacterium that naturally resides in the gastrointestinal tract, vagina, and rectum of many pregnant women. GBS is typically harmless and causes no symptoms. During pregnancy, it can pose serious risks if passed to a newborn during birth, potentially leading to life-threatening infections. Due to these risks, the American College of Obstetricians and Gynecologists recomenneds routine GBS testing for all pregnant women. If you test positive, ACOG has guidelines, like antibiotics during labor, to protect your baby. Ideally, preventing colonization with group B strep altogether would eliminate the risk of passing it to your baby during birth and remove the need for antibiotics during labor.

A study published in 2020 evaluated the potential of oral probiotics to eradicate a current vaginal GBS colonization. The study participants were women who tested positive for GBS. Women in the control group took a probiotic supplement with four strains of Lactobacillus twice daily for 14 days. In a follow-up GBS test, 63.6% of the control group was GBS positive compared to 77.8% in the placebo group. Although researchers observed a trend toward reduced GBS persistence after probiotic intake, it was not considered statistically significant.

A 2020 review concluded that there is limited evidence to recommend the regular use of probiotics to minimize the risk of GBS colonization. A 2022 systematic review and meta-analysis found probiotic administration during pregnancy, namely in the third trimester, was associated with a reduced GBS recto-vaginal colonization at 35–37 weeks and a safe perinatal profile. The same year, another systematic review and meta-analysis revealed that using a probiotic before becoming pregnant decreased the probability of a positive GBS result by 44%.

In a more recent 2023 study, researchers randomized pregnant women to take a probiotic or placebo once daily for 28 weeks. 20.4% of the placebo group tested positive for GBS at 36 weeks, compared to 15.4% in the probiotic group. Although there was a 5% reduction in GBS colonization, it did not reach statistical significance. Researchers did observe that the probiotic significantly reduced gastrointestinal symptoms of pregnancy compared with placebo. This aligns with much evidence on the benefits of probiotics and probiotic-rich foods.

As of April 2025, a double-blind, randomized, placebo-controlled clinical trial is underway to investigate whether using three specific species of probiotics taken orally in pregnancy from 25 weeks will reduce the incidence of GBS. Hopefully, that will give us more data on whether probiotics can reduce GBS.

Research requires clear standards to determine whether findings are statistically significant. While some studies may not meet this threshold, it’s important to recognize that they still suggest a slight risk reduction. If taking a daily probiotic has the potential to lower your risk of GBS and eliminate the risk to your baby and the need for antibiotics, it is worth considering.

See this episode to learn what to expect during GBS testing, how a positive result will impact your labor and birth, and explore more research on how probiotics could potentially reduce the chances of having GBS.

Preeclampsia

Preeclampsia is a serious pregnancy disorder associated with hypertension (high blood pressure). This condition is estimated to affect between 2-8% of pregnancies.

One study examined the association between consumption of milk-based probiotic products in pregnancy and the development of preeclampsia. This was part of the Norweigan Mother and Child Cohort study, which included over 33,000 participants. Researchers found that milk-based probiotic foods containing lactobacilli decreased the risk for preeclampsia.

A triple-blinded randomized controlled trial investigated a symbiotic (supplement with pre- and probiotics) for pregnant mothers with mild preeclampsia. The trial found that women taking synbiotics had significantly lower blood pressure than the placebo group. They also had a lower rate of severe preeclampsia, less protein in their urine, and better kidney function.

A systematic review and meta-analysis found limited evidence that probiotic supplementation affects the risk for preeclampsia. Like research on probiotics and constipation, there is not overwhelming evidence, but research does show it may decrease your risk or improve outcomes if you have preeclampsia.

Probiotics Following Antibiotics

Antibiotics are one of the most widely prescribed medications. You could take antibiotics during pregnancy to treat a UTI or other infection. Your doctor administers antibiotics during labor if you are positive for GBS or if you have a cesarean birth. After your baby is born, your doctor could prescribe an antibiotic for mastitis, which is an infection associated with breastfeeding. Since antibiotics kill both harmful and beneficial bacteria in your gut, it can take time for your gut microbiome to fully recover. Eating probiotic-rich foods or taking a probiotic after a course of antibiotics can help rebuild and rebalance your gut bacteria faster.

Taking a Probiotic Supplement

Ideally, you get every vitamin and nutrient you need from your diet. In reality, supplements can help fill gaps and ensure you are getting specific nutrients. Let’s discuss probiotic supplements and their side effects and safety.

Side Effects

Some common side effects of probiotics are digestive issues, which is ironic since many people take probiotics to improve digestion. It’s possible to experience symptoms like gas, bloating, or constipation when you first start a probiotic. The good news is that these symptoms usually disappear after a few weeks as your gut microbiome and body adjusts.

One way to minimize side effects is to start with a lower dose of probiotics and gradually increase to the recommended daily amount. Many supplements will include instructions to do this on the label. Everyone’s gut microbiome is different. If you experience side effects, you do not have to push through unwanted symptoms and can always stop taking the probiotic.

Also, if you have allergies to things like dairy, eggs, or soy, be sure to check the label carefully to avoid an allergic reaction.

Risks and Downsides

Evidence shows probiotics are generally considered safe and are well tolerated, even during pregnancy and breastfeeding. A theoretical concern with probiotics is the potential for the organisms they contain to cause a systemic infection. Although this has been reported in rare cases, it’s extremely uncommon. The risk of developing bacteremia (bacteria in the bloodstream) from taking Lactobacillus probiotics is estimated to be less than 1 in 1 million users. The risk of developing fungemia (fungus in the bloodstream) from Saccharomyces boulardii is even lower, with around 1 in 5.6 million users. These figures are thought to be even less likely in healthy individuals. The risk is the same whether you are pregnant or breastfeeding or not. As you can see, it is an extremely low, almost non-existent risk.

Probiotics and Breastfeeding

Evidence shows that mothers pass probiotics to their babies through breastfeeding. These bacteria may help protect the infant against infections and support the development of the immune system. Breast milk also contains sugars called human milk oligosaccharides. These sugars act as a prebiotic to feed the beneficial bacteria in the baby’s gut. A double-blinded, placebo-controlled study found administering probiotics to pregnant and lactating mothers increased the immunoprotective potential of breast milk and provided protection against atopic eczema during the first two years of life. Due to the evidence that pre- and probiotics are important for infant health, many infant formula companies also add pre- and probiotics to infant formula. However, breast milk is so complex that they still can’t fully replicate it.

Should You Take a Probiotic?

There is a lot of evidence that consuming probiotics benefits many aspects of your health. Pregnancy is when you need to be more mindful about your health and the health of your growing baby. There is research showing that probiotics are beneficial. While there may not be overwhelming evidence that probiotics can prevent issues like GBS or preeclampsia, even a slight reduction in your risk can be worth a relatively inexpensive and easy intervention. You already take a daily prenatal vitamin, so adding a probiotic wouldn’t be inconvenient. At the very minimum, you should include some probiotic-rich foods in your diet. If you take a probiotic with bothersome side effects, you can always stop taking it, and any side effects should subside.

Understanding Probiotic Labels

You can see there is quite a lot of evidence on the benefits of probiotics and little risk or downside. There are so many options of probiotic supplements available and choosing the right probiotic supplement can feel overwhelming. Learning how to read labels and what information to look for can help you narrow your choices and find the right one.

Most probiotic supplements combine different species of bacteria into a single product. These are broad-spectrum probiotics or multi-probiotics. The two most common species you will see on a probiotic label are Lactobacillus and Bifidobacterium. Lactobacillus bacteria produce lactase, an enzyme that breaks down lactose, the sugar in milk. They also produce lactic acid, which helps control the growth of harmful bacteria and improves your body’s absorption of minerals. Bifidobacterium species support the immune system, limit the growth of harmful bacteria in the intestine, and help break down lactose.

Each species has many different strains, and different strains can have different effects. For example, Lactobacillus acidophilus is a common strain; you might see it listed on a label as L. acidophilus. Since different strains target different symptoms or health issues, choosing a probiotic that contains strains suited to your specific needs is important. Based on the research covered in this episode, the most beneficial strains during pregnancy are Lactobacilli and Bifidobacterium.

Labels should also list the colony-forming units (CFUs), and you should look for a number in the billions. More CFUs aren’t always better, and the right strains at effective doses are more important than high numbers.

Choosing the Right Probiotic

In a comprehensive analysis of 48 widely sold probiotic supplements in the United States (67%) were found to be consistent in terms of their content and labeling information. That means one-third of the supplements included bacteria that weren’t listed on the label, didn’t actually contain the bacteria strains they claimed to have, or contained extremely low amounts (below 1%). These discrepancies result from manufacturing errors or poor quality control​. This highlights the importance of selecting a high-quality supplement from a reputable brand. A reputable manufacturer will have transparent labeling, third-party testing, and GMP (good manufacturing practices) certification to ensure what’s on the label is actually in the bottle.

Recommended Probiotics

I have done significant research on probiotics and supplements. There are a few I would recommend if you simply want a recommendation.

• AG1 is a fantastic source of pre and probiotics. This is my source of supplements for my gut health, and it also covers many other areas of health.
• If you prefer a supplement containing probiotics and not other vitamins, minerals, or nutrients, Garden of Life makes an excellent probiotic. This is one of my favorites based on many factors, including the probiotic strains, the brand, and the price.
• Garden of Life also has a probiotic specifically for pregnancy, which is a great option.

As with any supplement, please consult your doctor or midwife before taking it.

Thank you to the amazing companies that have supported this episode.