Health Watch: Caffeine and Miscarriages

Dr. Brett Parkinson with Mountain Medical breaks down the implications.

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Until recently the link between caffeine consumption and increased miscarriage rate was controversial: While some studies suggested that women who ingested large amounts of caffeine, usually more than 300 mg/day, suffered more miscarriages; other scientific inquiries failed to establish such a relationship. However, a new study, just published in the “The American Journal of Obstetrics and Gynecology,” suggests that pregnant women who consume more the than 200 milligrams or more of caffeine daily–the amount in 10 ounces of coffee or 25 ounces of tea–may double their risk of miscarriage. As a result of this new information the March of Dimes Web site just changed its advice to pregnant women, now advising them to limit their caffeine intake to 200 milligrams or less a day. Up until that time, their message was quite different as it indicated that 8 to 16 ounces of coffee a day was safe. The results of the new research confirm was Swedish scientists discovered in 2000, when they reported that women who drank five or more cups of coffee a day doubled their risk of miscarriage.

SUMMARY OF THE STUDY

• Data collected from pregnant women, 15 gestational weeks or less, in the San Francisco Kaiser Permanente Medical care program between 1996 and 1998

• Subjects interviewed about their consumption of caffeinated beverages, including coffee, tea, soda and hot chocolate

• Reports and medical records for pregnancy outcomes were followed through 20 weeks of gestation

• 1063 women participated in study, about 39% of those invited

• 25% reported no consumption, 60% between 0 to 200 mg/day, and 15% 200 mg/day or more

CAFFEINE CONTENT OF VARIOUS BEVERAGES IN MILLIGRAMS

• Coffee (drip), 155-175

• Coffee (brewed), 80-135

• Iced Tea, 47

• Hot tea (US), 40

• Hot tea (import), 60

• Hot cocoa 14

• Red Bull, 80

• Mountain Dew, 55

• Diet Coke, 45.6

• Dr. Pepper, 41

• Pepsi, 37.5

STUDY RESULTS (MISCARRIAGE RATES)

• No caffeine consumption, 12%

• 0 to 200 mg/day, 15%

• More than 200 mg/day, 25%

It is important to note that the study results hold true, no matter the type of caffeinated beverage consumed.

HOW DOES CAFFEINE AFFECT THE FETUS?

• It readily crosses the placental barrier

• Caffeine clearance is slower in pregnant women than in their non-pregnant counterparts

• Caffeine is also cleared slowly by the fetus

• Caffeine may reduce intervillous placental blood flow

Although some medical experts feel vindicated by the outcome of the new study, others are skeptical. In an interview with the “New York Times,” Dr. Carolyn Westhoff, a professor of obstetrics and gynecology and epidemiology at Columbia University Medical Center said that, because of the study design, she was not convinced that caffeine necessarily caused the miscarriages. She said, “Just interviewing women….does not strike me as the best way to get at the real scientific question here….But it is an excellent way to scare women.”

LIMITATIONS OF THE STUDY

• Women self-reported caffeine use, some after they had already miscarried, which could lead to recall bias

• Selection bias, due to fact 61% of women eligible for study elected not to participate

• While acknowledging that women who have morning sickness are less likely to miscarry (because hormonal changes that cause those symptoms contribute to a healthy pregnancy), Dr. DE-Kun Li, the lead researcher, indicated that “the observed association was not likely the the result of confounding by the pregnancy-related symptoms of nausea, vomiting, and aversion to caffeine consumption.” As reported in a recent “New York Times” article, some critics argue that the opposite may be true: “But some researchers said morning sickness could lead to confusing results in caffeine studies. These researchers argued that because they feel ill, some women may consume less caffeine. That tendency may make it appear that they are less like to miscarry because they avoid caffeine, when the reason is actually that they began with healthier pregnancies.”

Although the design of this study is not perfect, it does add to the growing body of evidence that caffeine is associated with an increased risk of miscarriage. Better to play it safe and minimize caffeine consumption during pregnancy. After all, there is no downside to decreasing or eliminating one’s intake of caffeine. Except that you may not feel quite so alert. A small price to pay for a successful pregnancy.

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ABOUT MOUNTAIN MEDICAL PHYSICIAN SPECIALISTS