Caffeine in miscarriages: it's not just in the coffee

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To the Editors:

We applaud the efforts of Weng et al¹ on caffeine consumption and risk of miscarriage. The effects of caffeine on risk of miscarriage have been highly debated. In a similar cohort study by Savitz et al² participants underwent a 1-time interview to ascertain caffeine exposure prepregnancy, 4 weeks after last menstrual period, and at the time of interview. Caffeine consumption at all 3 time points was found to be unrelated to miscarriage with all adjusted odds ratios between 0.7 and 1.3. One limitation of Weng et al's study was possible recall bias. It may have been more beneficial to have had the study participants submit daily or weekly caffeine intake diaries. People may over- or underestimate frequency/amount of caffeine intake. While the role of biological assays is unclear at this time, the half-life of caffeine is increased in pregnant women¹; thus, serial measurements of serum caffeine levels may have played a role in confirming frequency/amount of caffeine intake. It is also important to explore other sources of caffeine not defined by this study, eg, energy drinks. Our group has observed that the caffeine concentrations in energy drinks tend to be much higher than that of common soft drinks, with 8 oz servings ranging from 33 to 77 mg in several brands, including Red Bull, SoBe, and Amp.³ Current national guidelines do not address safe consumption of energy drinks during pregnancy, and no studies to date have assessed the influence of energy drinks on miscarriage. Of equal importance are hidden sources of caffeine, eg, decaffeinated coffee. Our group previously reported on the caffeine content of several brands of decaffeinated coffees, eg, Starbucks, Dunkin' Donuts, McDonald's, etc, and discovered a large range of caffeine concentrations (0-13.9 mg) per 16 oz serving size. Similarly, 6 cups of decaffeinated espresso from the same batch had caffeine concentrations ranging from 3 to 15.8 mg.⁴ Other hidden sources include Excedrin pain reliever, chocolate products, eg, milk, candy, etc, or coffee-flavored products, eg, yogurt and ice cream. To date, the literature is still inconclusive regarding the influence of caffeine on miscarriage. With the possibility of increased risk, it is best to err on the side of caution and recommend reducing (or eliminating) caffeine consumption during pregnancy. Pregnant women should be informed by their health care providers of possible sources of caffeine.

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References 

1. Weng X, Odouli R, Li D. Maternal caffeine consumption during pregnancy and the risk of miscarriage: a prospective cohort study. Am J Obstet Gynecol. 2008;198:279.e1–279.e8
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2. Savitz DA, Chan RL, Herring AH, Howards PP, Hartmann KE. Caffeine and miscarriage risk. Epidemiology. 2008;19:55–62
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3. McCusker RR, Goldberger BA, Cone EJ. Caffeine content of energy drinks, carbonated sodas, and other beverages. J Anal Toxicol. 2006;30:112–114
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4. McCusker RR, Fuehrlein B, Goldberger BA, Gold MS, Cone EJ. Caffeine content of decaffeinated coffee. J Anal Toxicol. 2006;30:611–613
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   • MEDLINE