We received a news report from a member about probiotics in pregnancy causing an increased risk of preeclampsia. Thank you for bringing this to our attention, Leah. We will not share the news report, because as happens entirely too often, the reporter does not fully understand the research, and the information is presented in a way to draw maximum attention.
I looked up the study in question (source). It was primarily focused on preventing gestational diabetes, not preeclampsia, but included data on other outcomes. It was a small study, around 400 participants identified as overweight or obese. Half were assigned to take probiotics while the other half received a placebo.
When you have a small sample size like this, it is possible that more patients who were going to have a better outcome anyway would end up in the treatment group just by luck. This can make it look like the treatment had a good effect when maybe it did not.
The opposite is also true--more patients who were already going to have a good outcome could end up in the placebo group by chance, making it look like the treatment was actually harmful when it was not. (But if the treatment group had worse outcomes, it is likely the treatment in question does not help, even if it does not hurt.)
This is why studies are repeated over and over with more and more participants. The larger the sample size, the harder it is for this to happen by chance, and the more likely the results are to be accurate. This is also why so many treatments that seemed to show promise in early, small studies are later found not to help after all.
It is true that this study found more cases of preeclampsia (almost double) among those taking probiotics compared with those taking placebos. Does this mean probiotics cause preeclampsia, or make it worse? Not necessarily. Again, this was a small study, and it is entirely possible that it was just bad luck that more participants who were going to get preeclampsia anyway ended up in the treatment group. I noticed that statistically, the placebo group had a lower rate of preeclampsia than we would expect, which would point to the "bad luck" explanation rather than probiotics being harmful. We would not conclude that placebo pills prevent preeclampsia, after all. But it is also pretty clear from the results that probiotics did not prevent preeclampsia or gestational diabetes.
So, what does this mean for you, our members? First of all, if you took probiotics and also got preeclampsia, I want to assure you that this was not your fault. You did not cause complications by taking probiotics.
For those of you currently pregnant or considering a pregnancy, it should be fine to eat yogurt, drink kefir, and other probiotic-containing foods if you enjoy them. Please check with your doctor before taking additional high-dose supplements of probiotics, just like you would any other supplement. And if you see people proclaiming all the amazing health benefits of high-dose probiotics? Take it with a grain of salt. The research so far does not support those claims.