TLDR: It isn’t fully clear if probiotics contribute to the risk of preeclampsia, but there is enough evidence to warrant caution around their use during pregnancy when there are preexisting health conditions. Always work with your healthcare provider on your individual best plan for supplements during pregnancy.
Preeclampsia is a serious health condition for pregnant women and their babies. Marked by high blood pressure and the potential to damage vital organs, the exact cause of preeclampsia is unknown. That said, it’s no surprise that moms-to-be want to do whatever they can to prevent it during their pregnancy.
A recent meta-analysis* found that taking probiotics during pregnancy may increase the risk of preeclampsia. After this study was published in a prestigious scientific journal, many news websites started to caution about the use of probiotics in pregnancy. Our team at Tiny Health heard about this concern and explored the evidence behind it. In this article we’ll cover:
- the basics of preeclampsia;
- the science behind the recent meta-analysis;
- and answer the question, are probiotics safe during pregnancy?
*A meta-analysis is like a super-powered summary of scientific studies. It combines data from various studies to give a clearer and more accurate picture of a specific topic.
First of all, what’s preeclampsia?
Preeclampsia, or ‘PreE’ is a condition that typically develops after the 20th week of pregnancy, however the majority of cases occur closer to term. And sometimes, preeclampsia can occur even after a baby is born, usually within 2 days of birth. It affects about 2-8% of pregnant women and varies in severity. The exact cause is not known but it’s believed to be related to problems with the placenta. It can be a significant health concern for both mom and her unborn baby [1].
The hallmark of preeclampsia is high blood pressure. Other symptoms of preeclampsia may include:
- Swelling due to liquid retention, particularly of the feet, legs, hands, and face
- Frequent, severe headaches that don’t respond to medication
- Visual disturbances. Some women experience blurry vision or sensitivity to light
- Severe, persistent pain in the upper abdomen, just below the ribs
At present, preeclampsia cannot be reliably predicted or prevented. But there are certain things that increase the chances of developing it.
Preeclampsia risk factors include:
- First pregnancy
- Having twins or more babies
- Having had preeclampsia in a previous pregnancy
- Chronic hypertension
- Pregestational diabetes or gestational diabetes
- A pre-pregnancy body mass index higher than 30
- Being 35 years or older
- If baby was conceived by in vitro fertilization [1]
That said, preeclampsia can occur in healthy pregnant women without any of these risk factors.
Preeclampsia is particularly dangerous because it can cause preterm birth, progress to eclampsia (which is preeclampsia with seizures) or to HELLP syndrome which is where the liver shows signs of damage.
It’s critical to share any symptoms you may have during your pregnancy or after delivery with your healthcare provider.
Results from the meta-analysis
The meta-analysis from Davidson et al. 2021 [2] concluded that probiotics during pregnancy significantly increase the risk of preeclampsia. This conclusion was drawn from the combination of four clinical trials. Here are some important facts about these studies:
All the women who participated in these studies were women with overweight or obesity.
An elevated body mass index before pregnancy is a known risk factor for gestational diabetes (GDM) and preeclampsia [3]. Recent research suggests that women with GDM or preeclampsia have a different gut microbiome than healthy women. So it’s possible that women with overweight obesity react differently to probiotic supplements, increasing their risk of complications.
Separately, none of the studies found that probiotics increased the risk of preeclampsia. Combined, preeclampsia cases were few.
Remember that the meta-analysis study combined the data from four studies. If we look at each of the studies individually, none of them concluded that probiotics increased the risk of preeclampsia. Also, the number of preeclampsia cases were few compared to the total number of participants. There were 31 cases of preeclampsia in 472 women who took probiotics, and 17 cases in the 483 women who took a placebo. This is a rate of 6.5% of cases in the probiotic group and 3.5% in the placebo group. Both of these are within the population incidence of preeclampsia, which is estimated to occur in 2-8% of pregnancies. Still, this is not a large number of cases.
Risk of preeclampsia was not the primary outcome of the study.
The studies analyzed in the meta-analysis focused first on the effect of probiotics on the risk of GDM. This association was the primary outcome they wanted to measure. Risk of preeclampsia was a secondary outcome, which means it was not the main focus of the studies.
When researchers choose a health condition as their study's primary outcome, like GDM in these studies, they try to consider all the risk factors involved in its development. They aim to balance the groups being studied (e.g., those taking probiotics and those taking a placebo) so that they have the same risk factors and characteristics. If both groups are balanced, then differences between the groups can be more strongly attributed to the different exposures in the study - in this case whether or not they were taking probiotics.
For the meta-analysis, preeclampsia was not the primary outcome studied. It’s possible that some risk factors specific for this condition were not considered or well-balanced between groups. For instance, none of the studies provided information about how the babies were conceived, and we know that in vitro fertilization is a risk factor for preeclampsia. Also, some of the studies didn’t specify how many women over 35 years old were included, and that’s another risk factor for preeclampsia [1].
The probiotic strains and dosage used differed among studies.
There are many different types of probiotics on the market. The studies analyzed used different probiotic strains (and dosage):
- A combination of Lacticaseibacillus rhamnosus GG and Bifidobacterium lactis BB12
- Ligilactobacillus salivarius UCC118
- A combination of Lacticaseibacillus rhamnosus HN001 and Bifidobacterium lactis 420
So, we can’t say there are specific probiotic strains that increase the risk of preeclampsia and ones that don’t. It would be ideal to only combine studies using the exact same strains and dosage, to clearly associate a type of probiotic with the increased risk. But this is something that researchers could explore in future clinical trials.
Results from other studies
A similar meta-analysis from 2022 assessed the risk of preeclampsia in women with overweight and obesity [4]. Like Davidson’s recent study [2], this newer meta-analysis looked at four clinical trials and also concluded that probiotics may increase the risk of preeclampsia. Three of these trials were the same studies included in Davidson’s.
One trial included in the 2022 analysis was slightly different, however. It looked at the effects of probiotic yogurt, which is clearly not the same as a probiotic capsule. When the authors took this study out of the meta-analysis, the results revealed that probiotics didn’t increase the risk of preeclampsia.
Are probiotics safe during pregnancy?
In regards to probiotics and the risk of preeclampsia - the data is not yet definitive. After reviewing the current science, we believe that women with preexisting health conditions like obesity should ask their healthcare provider before taking supplements or probiotics during pregnancy. One meta-analysis found an increased risk for preeclampsia in this specific population. This means that extra caution should be taken. At the same time, further studies need to be done.
Does this mean non-obese pregnant women should refrain from taking probiotics, too? We don’t think so. There isn’t evidence that probiotics increase a healthy woman’s risk of preeclampsia. That said, all pregnant women should discuss any supplements including pre and probiotics with their healthcare provider.
Depending on your particular situation, a probiotic can be a great supplement to take during pregnancy. Which one to choose will depend on your specific gut or vaginal microbiome composition and/or symptoms. Learn about your microbiome and get unbiased recommendations by taking a Tiny Health Microbiome Test.
