Caffeine Use in Pregnancy

Health Letter, June 2016

By Sarah Sorscher, J.D., M.P.H.

Pregnant women often face tough choices when it comes to selecting the right habits to ensure a healthy pregnancy. Whether or not to use caffeine is one of them: 97 percent of mothers consume caffeine before becoming pregnant, mainly from drinking coffee, soda and tea.[1] Yet very little information is available on the health impact of caffeine use during pregnancy on the mother and child.

Today, women are often advised to reduce or avoid caffeine use during pregnancy. Accordingly, the amount of caffeine consumed by pregnant women has fallen over the past two decades,[2] to the point where now nearly 80 percent of expectant mothers decrease their caffeine consumption or stop altogether during pregnancy.[3] But this popular habit can prove difficult to kick, leading many women to ask: How much caffeine is really safe during pregnancy?

Processing caffeine during pregnancy

A pregnant woman’s ability to process caffeine decreases over the course of her pregnancy. Pregnant women take twice as long to process the same amount of caffeine in the third trimester than in the first trimester.[4]

Caffeine consumed by the mother passes through the placenta and into the bloodstream of the fetus. Fetuses also have a reduced ability to process caffeine because they lack the main liver enzyme used to do so.[5] There is also some evidence that caffeine decreases blood flow to the placenta, although this remains debated.[6],[7]

However, the actual effects of caffeine exposure on the developing fetus are unclear, and additional clinical studies are needed to show whether caffeine influences such things as fetal growth, length of gestation, chances of miscarriage or even child development beyond birth.

Good data is hard to find

Caffeine consumption, like many lifestyle choices during pregnancy, can be difficult to study because it is nearly impossible to separate caffeine use from other habits and characteristics that may affect a woman’s pregnancy.

For example, women who are generally health-conscious may be more likely to eliminate use of caffeine and other drugs and simultaneously engage in healthy eating and exercise habits during pregnancy. This makes it hard for researchers to know whether it was decreased caffeine use or other positive health habits that caused the women to have a healthy and normal pregnancy and birth.

Researchers try to address this problem by making adjustments for factors that could influence the pregnancy, such as a mother’s education level, ethnicity, vitamin use, smoking, alcohol use, and height and weight.[8] But there is always a chance that researchers have not accounted for every factor that could have affected a pregnancy.

Another problem that can lead to confusing results is that many studies involving caffeine enroll women who already have experienced a negative pregnancy outcome, such as a miscarriage, and ask them to remember their dietary habits during pregnancy. These responses are then compared to responses from a group of women who had healthy pregnancies.

Women who have had a miscarriage, birth defect, or other poor pregnancy outcome may be more likely to rack their memories for any bit of information about their habits during pregnancy that could help to explain what happened. This could lead to caffeine use being reported more by women who have had an adverse pregnancy outcome compared to those who did not, a phenomenon known as recall bias.[9]

For these reasons, experts tend to lend the greatest weight to randomized, controlled trials, which eliminate the possibility of these types of problems by randomly assigning women to receive a particular intervention (in this case caffeine use). However, randomly changing pregnant women’s lifestyle habits can be scientifically challenging and in some cases unethical.

Not surprisingly, only one randomized, controlled clinical trial that tested the impact of different levels of caffeine consumption on pregnancy outcomes has been published.[10] That study, carried out in Denmark, involved just over 1,200 coffee-drinking pregnant women and looked at the impact of caffeine on birth weight and length of gestation.[11] The researchers randomly assigned women to receive either regular or decaffeinated instant coffee, to be drunk instead of their usual coffee.

At the end of the Danish study, women in the decaf group had consumed less caffeine than those in the caffeinated coffee group; about 120 mg versus 320 mg, on average. (Women in both groups were allowed to drink additional coffee, tea, soda or hot chocolate throughout the study, and were asked to report this information to the researchers.[12]) Yet this difference in caffeine consumption did not lead to any differences in terms of birth weight or length of gestation.[13]

However, the fact that one randomized study failed to show an adverse effect of caffeine does not necessarily mean caffeine is safe during pregnancy. It is possible that the study was too small to detect rare risks, or that the differences in caffeine consumption were too small to cause measurable effects.

Risk of miscarriage

In contrast to the single randomized, controlled trial, other studies have indicated that caffeine does have negative effects on at least one important pregnancy outcome: miscarriage.

Most, but not all, studies tracking women’s habits from the beginning of their pregnancies (as opposed to asking women to think back after a bad outcome has already occurred) have found that high levels of caffeine consumption are associated with a higher risk of miscarriage.[14] For example, a study of a little over 1,000 women who were interviewed about their caffeine habits during the first trimester of pregnancy found that women who drank 200 mg of caffeine or more per day were twice as likely to have a miscarriage compared with women who drank no caffeine.[15] Another study looked at the combined results of 14 publications analyzing over 130,000 women’s dietary habits during their pregnancies, and found a 40-72 percent increased risk of miscarriage among women who drank 350 mg or more of caffeine per day compared with those who had no or very low (less than 50 mg per day) caffeine intake.[16]

Other pregnancy outcomes

Many additional studies looking at the effect of caffeine on other pregnancy outcomes found conflicting results. For example, some studies showed that caffeine consumption increases the risk of preterm birth, whereas other studies found no such increased risk. Of note, a recent analysis that pooled data from 22 different studies found no increased risk of preterm birth associated with caffeine consumption.[17]

The effects of caffeine on infant birth weight also have been frequently studied. Several large studies that tracked women’s habits during pregnancy have suggested that women who consume 200 mg of caffeine or more per day are more likely to have babies with low birth weight (although other studies showed no effect of caffeine consumption on birth weight).[18],[19],[20]

Additional effects of maternal caffeine consumption during pregnancy on children following birth, including effects on child IQ and the risk of childhood obesity, also generally have failed to yield consistent results.[21],[22],[23],[24]

What you should do

In light of the existing evidence, there is uncertainty about what amount of caffeine is safe to consume during pregnancy. But given the fact that both pregnant women and fetuses have a reduced ability to process caffeine, and because some studies have suggested that caffeine consumption increases the risk of miscarriages, the safest course of action is for women to strive to limit caffeine intake — or eliminate it entirely — during pregnancy.

The American College of Obstetricians and Gynecologists has stated that moderate caffeine intake of less than 200 mg per day is unlikely to have a big impact on risk of miscarriage or preterm birth, but the physician’s group could not draw conclusions about the safety of higher amounts of caffeine.[25]

To avoid potential risks, pregnant women who cannot manage to eliminate caffeine entirely should aim to keep consumption below 200 mg per day.

In estimating your caffeine intake, remember that coffee, tea and other beverages often vary widely in the amount of caffeine they contain, even for the same type of beverage. For example, frequently cited figures from the U.S. Department of Agriculture indicate that an average eight-ounce cup of brewed coffee contains 137 mg of caffeine.[26] The popular coffee chain Starbucks, however, estimates that a single eight-ounce cup of its brewed coffee contains 180 mg of caffeine.[27] Given this range, aiming for one eight-ounce cup of coffee a day or less will likely keep most women below the 200 mg per day limit, assuming coffee is their only caffeine source.

The chart below provides more information on the approximate caffeine content of different kinds of coffee, tea, soda and chocolate.

Caffeine Content of Foods and Beverages [28]

Food and Beverages Milligrams of Caffeine (Average)
Coffee (8 oz.)
Brewed, drip 137[29]
Instant 76[30]
Tea (8 oz.)
Brewed 48[31]
Instant 26 – 36[32]
Soda
Regular cola (12 oz.) 34[33]
Diet cola (12 oz.) 46[34]
Chocolate
Dark chocolate (1.45 oz.) 30[35]
Milk chocolate (1.55 oz.) 11[36]
Semi-sweet chocolate (¼ cup) 26 – 28[37]
Chocolate syrup (1 tbsp.) 3[38]
Hot cocoa (12 oz.) 8 – 12[39]

References

[1] Chen L, Bell EM, Brown ML, et al. Exploring maternal patterns of dietary caffeine consumption before conception and during pregnancy. Matern Child Health J. 2014;18:2446-2445.

[2] Ibid.

[3] Ibid.

[4] Maslova E, Sayanti B, Lin SW, Michels KB. Caffeine consumption during pregnancy and risk of preterm birth: A meta-analysis. Am J Clin Nutr. 2010;92:1120-1132.

[5] Bakker R, Steegers EA, Obradov A, et al. Maternal caffeine intake from coffee and tea, fetal growth, and the risks of adverse birth outcomes: The Generation R Study. Am J Clin Nutr. 2010;91:1691-1698.

[6] CARE Study Group. Maternal caffeine intake during pregnancy and risk of fetal growth restriction: A large prospective observational study. BMJ. 2008;337:a2332.

[7] American College of Obstetricians and Gynecologists. Committee opinion: Moderate caffeine consumption during pregnancy. Obstet Gynecol. 2010;116(2):467-468.

[8] Bakker R, Steegers EA, Obradov A, et al. Maternal caffeine intake from coffee and tea, fetal growth, and the risks of adverse birth outcomes: The Generation R Study. Am J Clin Nutr. 2010;91:1691-1698.

[9] Rockenbauer M, Olsen J, Czeizel A, et al. Recall bias in a case-control surveillance system on the use of medicine during pregnancy. Epidemiology. 2001;12(4):461-466.

[10] Jahanfar S, Jaafar SH. Effects of restricted caffeine intake by mother on fetal, neonatal and pregnancy outcomes. Cochrane Database of Systematic Reviews. 2015;(6). Art. No.: CD006965.

[11] Bech BH, Obel C, Brink H, Olsen J. Effect of reducing caffeine intake on birth weight and length of gestation: Randomized controlled trial. BMJ. 2007;334(7590):409.

[12] Ibid.

[13] Ibid.

[14] Hahn KA, Wise LA, Rothman KJ, et al. Caffeine and caffeinated beverage consumption and risk of spontaneous abortion. Human Reproduction. 2015;30(5):1246-1255.

[15] Weng X, Odouli R, De-Kun L. Maternal caffeine consumption during pregnancy and the risk of miscarriage: A prospective cohort study. Am J Obstet Gynecol. 2008;198(3):279.e1-8.

[16] Chen LW, Wu Y, Neelakantan N, et al. Maternal caffeine intake during pregnancy and risk of pregnancy loss: A categorical and dose-response meta-analysis of prospective studies. Public Health Nutr. 2016;19(7):1233-1244.

[17] Maslova E, Bhattacharya S, Lin SW, Michels KB. Caffeine consumption during pregnancy and risk of preterm birth: a meta-analysis. Am J Clin Nutr. 2010;92:1120-1132.

[18] CARE Study Group. Maternal caffeine intake during pregnancy and risk of fetal growth restriction: A large prospective observational study. BMJ. 2008;337:a2332.

[19] Bakker R, Steegers EA, Obradov A, et al. Maternal caffeine intake from coffee and tea, fetal growth, and the risks of adverse birth outcomes: The Generation R Study. Am J Clin Nutr. 2010;91:1691-1698.

[20] Sengpiel V, Elind E, Bacelis J, et al. Maternal caffeine intake during pregnancy is associated with birth weight but not with gestational length: Results from a large prospective observational cohort study. BMC Medicine. 2013;11:42.

[21] Galéra C, Bernard J, van der Waerden J, et al. Prenatal caffeine exposure and child IQ at age 5.5 years: The EDEN mother-child cohort. Biol Psychiatry. 2015; pii: S0006-3223(15)00733-7. doi: 10.1016/j.biopsych.2015.08.034.

[22] Li D-K, Ferber JR, Odouli R. Maternal caffeine intake during pregnancy and risk of obesity in offspring: A prospective cohort study. Int J Obes. 2015;39(4):658-664.

[23] Voerman E, Jaddoe VW, Gishti O, et al. Maternal caffeine intake during pregnancy, early growth, and body fat distribution at school age. Obesity. 2016. doi: 10.1002/oby.21466.

[24] Klebanoff MA, Keim SA. Maternal serum paraxanthine during pregnancy and offspring body mass index at ages 4 and 7 years. Epidemiology. 2015;26(2):185-191.

[25] The American College of Obstetricians and Gynecologists. Committee Opinion: Moderate caffeine consumption during pregnancy. Obstet Gynecol. 2010;116(2):467-468.

[26] Ibid.

[27] Starbucks.com. Pike Place Roast. http://www.starbucks.com/menu/drinks/brewed-coffee/pike-place-roast#size=1.

[28] American College of Obstetricians and Gynecologists. Committee Opinion: Moderate caffeine consumption during pregnancy. Obstet Gynecol. 2010;116(2):467-468.

[29] Ibid.

[30] Ibid.

[31] Ibid.

[32] Ibid.

[33] Coca-Cola Product Facts. Coca-Cola. http://www.coca-colaproductfacts.com/en/coca-cola-products/coca-cola/.

[34] Coca-Cola Product Facts. Diet Coke. http://www.coca-colaproductfacts.com/en/coca-cola-products/diet-coke/.

[35] American College of Obstetricians and Gynecologists. Committee Opinion: Moderate caffeine consumption during pregnancy. Obstet Gynecol. 2010;116(2):467-468.

[36] Ibid.

[37] Ibid.

[38] Ibid.

[39] Ibid