Moderate Caffeine Consumption During Pregnancy Does Not Increase Miscarriage Risk
Nov. 24, 1999 (New York) -- Pregnant women who can't seem to give up their
morning cup of coffee or tea may be interested in the results of a new study
showing that moderate caffeine consumption does not increase the risk of
miscarriage. Although some studies have indicated that caffeine could increase
the risk of miscarriage, this study, appearing in the Nov. 25 issue of
TheNew England Journal of Medicine, found that rates were only
affected in women who consumed caffeine in amounts equivalent to more than five
cups of coffee per day.
The study consisted of blood samples obtained from pregnant women enrolled
in the Collaborative Perinatal Project, which was conducted from 1959 to 1966.
Serum paraxanthine, the primary by-product of caffeine, was measured in almost
600 women who had miscarriages at less than 140 days into their pregnancy. They
compared them to nearly 2,600 women who gave birth to live infants at 28 weeks'
gestation or later and had blood drawn on the same day of gestation as the
women who miscarried. They found the mean serum paraxanthine concentration was
higher in the women who had miscarriages than in the other women.
"The reason we decided to use this particular database was because
per-capita coffee consumption in the U.S. peaked around 1962, so it was
convenient that we were able to access a database of pregnant women who were
pregnant predominantly in the early 1960s," the study's lead author, Mark
A. Klebanoff, MD, MPH, tells WebMD. "More recent studies have actually had
a hard time recruiting large numbers of women who consumed large amounts of
caffeine while pregnant." Klebanoff is a medical officer at the National
Institute of Child Health and Human Development, in Bethesda, Md.
Women with paraxanthine levels higher than 1,845 nanograms per milliliter of
blood had the greatest increased risk of miscarriage. Those with concentrations
above 1,845 nanograms per milliliter had nearly double the risk.
Klebanoff says a conservative estimate would be that more than five cups of
coffee per day would be needed to achieve a blood level of 1,845 nanograms per
milliliter or higher. A typical cup of brewed coffee has about 100 milligrams
of caffeine and a cup of tea has about 40 milligrams.
Caffeine is a stimulant that crosses the placenta, meaning it easily passes
from mother to child. Based largely on data from animal studies showing harmful
effects of caffeine on fetuses, the FDA has advised since 1981 that pregnant
women "avoid caffeine-containing foods and drugs, if possible, or consume
them only sparingly."
But as Brenda Eskinazi, PhD, points out in an editorial accompanying
Klebanoff's study, most pregnant women do not heed this advice. "In part
because of our own dependence on our morning cup of coffee, and because of our
inability to find strong associations with effects on health in humans, we have
accepted that more than 75% of pregnant women consume caffeinated
beverages," writes Eskinazi, of the University of California School of
Public Health, Berkeley. She says health care providers should continue to
counsel women who are pregnant or breast-feeding to limit their caffeine
intake. Eskinazi also points out that in addition to the risk of miscarriage,
caffeine has been linked in animal and human studies to changes in fetal heart
rate and breathing patterns, decreased brain weight and alterations in brain
development, learning and memory.
"We only looked at risk of spontaneous abortions [miscarriages] in this
study and we didn't see any increased risk until women were consuming very
large amounts of caffeine," Klebanoff says. "So it seems to me that the
best advice is that moderation in all things is always a good idea, but there
are probably more important things for pregnant women to worry about than
whether they are having a cup of coffee or two a day or a cup of tea or two a