High doses of daily caffeine during pregnancy -- whether from coffee, tea, caffeinated soda or hot chocolate -- cause an increased risk of miscarriage, according a new study by the Kaiser Permanente Division of Research. The study controlled, for the first time, pregnancy-related symptoms of nausea, vomiting and caffeine aversion that tended to interfere with the determination of caffeine's true effect on miscarriage risk. The research appears in the current online issue of American Journal of Obstetrics and Gynecology.
While previous research showed a link between caffeine consumption and
miscarriage, this is the first study to thoroughly control for morning
sickness, which typically causes many women to avoid caffeine, explained
De-Kun Li, MD, Ph.D., an investigator with the Kaiser Permanente Division
of Research and lead investigator of the study. "This study strengthens the
association between caffeine and miscarriage risk because it removes
speculation that the association was due to reduced caffeine intake by
healthy pregnant women," Li said.
To address that speculation, the study, which looked at 1,063 pregnant
Kaiser Permanente members in San Francisco from October 1996 through
October 1998, examined the caffeine effect among women who never changed
their pattern of caffeine consumption during their pregnancy. Kaiser
Permanente is the nation's largest health plan with 8.7 million members,
416 medical offices and 32 hospitals in nine states and the District of
Columbia.
Women who consumed 200 mg or more of caffeine per day (two or more cups
of regular coffee or five 12-ounce cans of caffeinated soda) had twice the
miscarriage risk as women who consumed no caffeine, said Li.
The increased risk of miscarriage appeared to be due to the caffeine
itself, rather than other possible chemicals in coffee because caffeine
intake from non-coffee sources such as caffeinated soda, tea and hot
chocolate showed a similar increased risk of miscarriage.
"The main message for pregnant women from these findings is that they
probably should consider stopping caffeine consumption during pregnancy
because this research provides clearer and stronger evidence that high
doses of caffeine intake during pregnancy can increase the risk of
miscarriage," said Li.
The reasons that caffeine can harm a fetus have been suspected for some
time. Caffeine crosses through the placenta to the fetus, but can be
difficult for the fetus to metabolize because of the under-developed
metabolic system. Caffeine also may influence cell development and decrease
placental blood flow, which may lead to an adverse effect on fetal
development.
Women in the study were asked about their intake of caffeinated
beverages as well as the type of their drinks, timing of initial drink, the
frequency and amount of intake, and whether they changed consumption
patterns since becoming pregnant. Sources of caffeine included coffee, tea,
caffeinated soda and hot chocolate.
Researchers estimated the amount of caffeine intake in various types of
beverages using the following conversion: For every 150 milliliters of
beverage, 100 milligrams for caffeinated coffee, 2 milligrams for
decaffeinated coffee, 39 milligrams for caffeinated tea, 15 milligrams for
caffeinated soda, and 2 milligrams for hot chocolate. Information on other
potential risk factors for miscarriage -- including maternal age, race,
education, household income, marital status, smoking, alcohol consumption,
hot tub use, exposure to magnetic fields during pregnancy, and symptoms
related to pregnancy such as nausea and vomiting -- also were collected
during the in-person interview and controlled during analyses. Pregnancy
outcomes up to 20 weeks of gestation were determined for all participants.
Overall, 172 of women in the study (16.18 percent) miscarried. Whereas
264 women (25 percent) reported no consumption of any caffeine containing
beverages during pregnancy, 635 women (60 percent) reported 0-200 mg of
caffeine intake per day, and 164 women (15 percent) had 200 mg or more of
daily caffeine consumption.
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