How Much Caffeine Is Safe During Pregnancy?

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Pregnancy greatly reduces our ability to metabolize caffeine.

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Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Dennis may be referring, watch the above video.

Is caffeine safe during pregnancy? Pregnancy greatly reduces our ability to metabolize caffeine. For example, in a typical adult, caffeine blood levels fall by about half, also known as the “half-life,” in five hours. As you reach mid-pregnancy, that time doubles and by the time you reach the third trimester, it can take 15 hours (or more!) to reduce caffeine to a similar level. At the same time, fatigue is one of the most common complaints of pregnant women. Couldn’t a little extra energy boost from slowly metabolizing caffeine be a good thing? Unfortunately, caffeine readily passes through the placenta, and if you think expecting moms metabolize slowly, babies have even less capacity to metabolize caffeine, with a half-life of 80 hours; that’s more than three days! But to what effect? In pregnancy, is caffeine a friend or foe?

Respected authorities, including the World Health Organization, the European Food Safety Authority, and The American College of Obstetrics and Gynecology have guidelines for a “positive pregnancy experience,” including restricting caffeine intake to reduce the risk of pregnancy loss and low birth weights. Higher caffeine intake pre-pregnancy is associated with higher risk of miscarriages, and higher intake during pregnancy is associated with low birth weight, so the World Health Organization suggests reducing consumption to less than 300 mg of caffeine a day, whereas the European Food Safety Authority suggests 200 mg per day may be the safety limit, in agreement with The American College of Obstetrics and Gynecology. That comes out to about two cups (480 ml) of brewed coffee a day, assuming that’s your sole caffeine source.

Since those guidelines were issued, this study of 2,000 moms found that even just a half cup of coffee (120 ml) or so a day was associated with a lower birth weight by about two ounces (60 g), which suggests that exposure to even less than 100 mg of caffeine may be associated with decreased fetal growth. The question is: Is it cause and effect? Is there something about caffeine that’s doing it, or something about caffeine drinkers? You can’t know unless you put it to the test. Or in this case, do a Mendelian randomization study, which is kind of a proxy for a randomized controlled trial, since due to the luck of the draw with genes, some people randomly have a tendency to drink more or less coffee throughout their life. And it did not find a strong relationship between genetic determinants of coffee consumption and these adverse outcomes, so it isn’t clear if the links that have been found are causal. There appears to have only been one randomized controlled trial that tried to test it.

More than a thousand coffee-drinking pregnant women were randomized to caffeinated coffee or decaf at an average of four months into their pregnancies. To improve compliance, they were just asked to switch to the provided coffee without being prescribed a specific caffeine intake. But thanks to the complimentary coffee, the women in the decaf group ended up consuming 200 fewer mg of caffeine a day than those in the caffeinated coffee group. So, in the end, the decaf group complied with the recommendation of getting less than 200 to 300 mg of caffeine a day, and the caffeine group did not. Was there any difference in birthweight or length of pregnancy between the two? No. Is it possible the women were all getting more than some threshold amount? We don’t know. I’m sympathetic to the view that says look, “the need for caution is compelling,” so we should err on the side of caution and tell women contemplating pregnancy, or who are pregnant, to avoid it completely. But women should realize that the evidence implicating caffeine in birth outcomes is far from settled.

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Motion graphics by Avo Media

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Dennis may be referring, watch the above video.

Is caffeine safe during pregnancy? Pregnancy greatly reduces our ability to metabolize caffeine. For example, in a typical adult, caffeine blood levels fall by about half, also known as the “half-life,” in five hours. As you reach mid-pregnancy, that time doubles and by the time you reach the third trimester, it can take 15 hours (or more!) to reduce caffeine to a similar level. At the same time, fatigue is one of the most common complaints of pregnant women. Couldn’t a little extra energy boost from slowly metabolizing caffeine be a good thing? Unfortunately, caffeine readily passes through the placenta, and if you think expecting moms metabolize slowly, babies have even less capacity to metabolize caffeine, with a half-life of 80 hours; that’s more than three days! But to what effect? In pregnancy, is caffeine a friend or foe?

Respected authorities, including the World Health Organization, the European Food Safety Authority, and The American College of Obstetrics and Gynecology have guidelines for a “positive pregnancy experience,” including restricting caffeine intake to reduce the risk of pregnancy loss and low birth weights. Higher caffeine intake pre-pregnancy is associated with higher risk of miscarriages, and higher intake during pregnancy is associated with low birth weight, so the World Health Organization suggests reducing consumption to less than 300 mg of caffeine a day, whereas the European Food Safety Authority suggests 200 mg per day may be the safety limit, in agreement with The American College of Obstetrics and Gynecology. That comes out to about two cups (480 ml) of brewed coffee a day, assuming that’s your sole caffeine source.

Since those guidelines were issued, this study of 2,000 moms found that even just a half cup of coffee (120 ml) or so a day was associated with a lower birth weight by about two ounces (60 g), which suggests that exposure to even less than 100 mg of caffeine may be associated with decreased fetal growth. The question is: Is it cause and effect? Is there something about caffeine that’s doing it, or something about caffeine drinkers? You can’t know unless you put it to the test. Or in this case, do a Mendelian randomization study, which is kind of a proxy for a randomized controlled trial, since due to the luck of the draw with genes, some people randomly have a tendency to drink more or less coffee throughout their life. And it did not find a strong relationship between genetic determinants of coffee consumption and these adverse outcomes, so it isn’t clear if the links that have been found are causal. There appears to have only been one randomized controlled trial that tried to test it.

More than a thousand coffee-drinking pregnant women were randomized to caffeinated coffee or decaf at an average of four months into their pregnancies. To improve compliance, they were just asked to switch to the provided coffee without being prescribed a specific caffeine intake. But thanks to the complimentary coffee, the women in the decaf group ended up consuming 200 fewer mg of caffeine a day than those in the caffeinated coffee group. So, in the end, the decaf group complied with the recommendation of getting less than 200 to 300 mg of caffeine a day, and the caffeine group did not. Was there any difference in birthweight or length of pregnancy between the two? No. Is it possible the women were all getting more than some threshold amount? We don’t know. I’m sympathetic to the view that says look, “the need for caution is compelling,” so we should err on the side of caution and tell women contemplating pregnancy, or who are pregnant, to avoid it completely. But women should realize that the evidence implicating caffeine in birth outcomes is far from settled.

Please consider volunteering to help out on the site.

Motion graphics by Avo Media

Doctor's Note

A note from Dr. Greger:

I am thrilled to introduce Dr. Kristine Dennis, our Senior Research Scientist. Dr. Dennis is an experienced nutrition and public health scientist who joined NutritionFacts to expand our research capacity — diving deep into the research, writing scripts, and now, narrating her own videos! You’ll continue to see videos from both of us interspersed in no particular order. I’m so happy Kristine is with NutritionFacts to help expand our capacity and perspectives.

We have many more videos on pregnancy. See the topic page. 

Are There Risks and Benefits of Energy Drinks? Check out the video. 

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