Quick answer

A review of 11 trials in 1,505 pregnant women found no change in cesarean births, birth weight or length of pregnancy with Lactobacillus and Bifidobacterium probiotics, and a second review found no serious problems. No trial tested Saccharomyces yeast. Ask your doctor before taking one, especially with a weakened immune system.^1,2

Key facts

A 2009 review pooled 11 randomized trials of Lactobacillus and Bifidobacterium probiotics in 1,505 pregnant women and found no effect on cesarean births, birth weight or length of pregnancy.¹
No randomized trial tested Saccharomyces yeast probiotics in pregnancy, so their safety there is unknown.¹
A 2021 review of 100 studies found no deaths or serious adverse effects, but only 11 of the studies reported adverse effects at all.²
One trial reported more vaginal discharge and changes in stool with a mix of Lactobacillus rhamnosus and L. reuteri.²
NIH says probiotics might cause infections in people who are seriously ill or have weak immune systems.³

What do trials in pregnant women show?

The two systematic reviews that speak to this question looked mainly at randomized trials in which pregnant women took probiotics or placebo. The older review, from 2009, searched databases up to September 2007. It found that Lactobacillus and Bifidobacterium products did not change the rate of cesarean birth, birth weight or gestational age, and that no malformations were reported in the probiotic groups. It found no miscarriage data to analyze.¹

In trials in pregnancy, Lactobacillus and Bifidobacterium probiotics did not change rates of cesarean birth, birth weight or length of pregnancy, and a 2021 review found no serious problems for mother or infant. One study reported more vaginal discharge and changes in stool with L. rhamnosus and L. reuteri. No trials have tested Saccharomyces yeast in pregnancy, so its safety there is unknown.^1,2

The newer review, from 2021, widened the search to prebiotics and synbiotics and to the weeks after birth. It counted 20 kinds of adverse effect across 11 studies, most of them stomach and bowel symptoms in the mother, such as nausea, diarrhea, constipation and bloating.²

What do these reviews leave out?

The gaps matter as much as the findings. About half of the 100 studies in the 2021 review said nothing about safety, and of the 11 that reported adverse effects, most did not say when they began or how severe they were. The trials also used many different strains, doses and start times, from the first trimester to a year after birth, so a result for one product does not carry over to another.^2,4

The review's authors pointed out that nausea, constipation and reflux are common in pregnancy anyway, and that their analysis did not find those problems more common with probiotics. Even so, a review of trials cannot rule out a rare harm.²

What do NIH and NCCIH say?

NIH's consumer fact sheet says there are no official recommendations that cover probiotic use by healthy people, and it suggests asking a health care provider which probiotic to choose, what dose to take and how long to use it. It adds that probiotics might not be safe for everyone, naming people who are seriously ill and people with weak immune systems.³

NCCIH says few studies have looked at probiotic safety in detail, so how often side effects occur is not well known, and it advises talking with a health care provider first, especially for anyone with health problems.⁴

Some probiotic products have been reported to contain microorganisms other than those listed on the label.⁴

Who should ask their doctor before taking a probiotic while pregnant?

Anyone with a weakened immune system should ask their doctor first, because NIH says probiotics might cause infections in people with weak immune systems.^3,5
People who are seriously ill or in hospital should ask a doctor, because the rare serious infections linked to probiotics were mostly in severely ill people.^4,6
Anyone considering a product that contains Saccharomyces, a yeast, should ask their doctor, because no trial has tested it in pregnancy.¹
People taking an antibiotic or an antifungal medicine can ask their pharmacist whether it changes anything, because NIH says those medicines might reduce a probiotic's effect.⁷
Anyone with a fever, vomiting, bloody diarrhea or severe belly pain during pregnancy should ask a doctor, because those need a diagnosis and not a supplement.

Questions people ask

Is probiotics safe during pregnancy?

Two systematic reviews of trials found no serious harm from Lactobacillus and Bifidobacterium probiotics in pregnant women. They could not speak for every strain or product, so ask your doctor before taking one.^1,2

Is probiotics ok during pregnancy if the strain was not in the studies?

The reviews tested particular strains, and NCCIH says a result for one probiotic does not carry over to another. Ask your doctor about the strains on your label.^2,4

Is a probiotic yeast such as Saccharomyces ok during pregnancy?

No randomized trial has tested Saccharomyces in pregnancy, so its safety there is unknown. Ask your doctor before using a product that contains it.¹

Can probiotics cause vaginal discharge or loose stools in pregnancy?

One trial of Lactobacillus rhamnosus with L. reuteri reported more vaginal discharge and changes in stool than with placebo. The reviews found no serious problems for mother or infant.²

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This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.