Too much caffeine during pregnancy may increase the risk of
miscarriage, a new study says, and it suggests that pregnant women
may want to reduce their intake or cut it out entirely.
Many obstetricians already advise women to limit caffeine, though
the subject has long been contentious, with conflicting studies,
fuzzy data and various recommendations given over the years.
The new study, being published Monday in the Journal of
Obstetrics and Gynecology, finds that pregnant women who consume 200
milligrams or more of caffeine a day - the amount in 10 ounces of
coffee or 25 ounces of tea - may double their risk of miscarriage.
Ten ounces is equivalent to about 300 milliliters.
Pregnant women should try to give up caffeine for at least the
first 3 or 4 months, said the lead author of the study, Dr. De-Kun
Li, a reproductive and perinatal epidemiologist at the Kaiser
Permanente Division of Research in Oakland, California.
"If, for whatever reason, they really can't do it, think of
cutting to one cup or switching to decaf," Li said. "Stopping
caffeine really doesn't have any downside."
Professional groups like the American College of Obstetricians
and Gynecologists and the American Society for Reproductive Medicine
have not taken official positions on caffeine, representatives said.
On Friday, the March of Dimes Web site said most experts agreed
that the amount of caffeine found in 8 to 16 ounces of coffee a day
was safe. It noted that some studies had linked higher amounts to
miscarriage and low birth weight, but stated: "However, there is no
solid proof that caffeine causes these problems. Until more is
known, women should limit their caffeine intake during pregnancy."
Now, having reviewed the new study, the March of Dimes plans to
change its message, to advise women who are pregnant or trying to
conceive to limit their daily caffeine intake to 200 milligrams or
less, said Janis Biermann, its senior vice president of education
and health promotion.
Li's study included 1,063 pregnant women who were interviewed
once about their caffeine intake. At the time of the interview,
their median length of pregnancy was 71 days. But 102 had already
miscarried - not surprising, because most miscarriages occur very
early in pregnancy. Later, 70 more women miscarried, for an overall
miscarriage rate of 16 percent for the group, a typical rate.
Of 264 women who said they used no caffeine, 12.5 percent had
miscarriages. But the miscarriage rate was 24.5 percent in the 164
women who consumed 200 milligrams or more per day. The increased
risk was associated with caffeine itself and not with other known
risk factors like the mother's age or smoking habits, the
researchers said.
Li said the study had answered an important question that
previous research had left unresolved. Women who have morning
sickness are less likely to miscarry than those who do not, possibly
because the same hormonal changes that cause nausea and vomiting
contribute to a healthy pregnancy. But some researchers said morning
sickness could lead to misleading 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 likely to miscarry because they avoid caffeine, when
the real reason is actually that they started out with healthier
pregnancies.
Li said he and his colleagues had carefully analyzed the data and
determined that the risk from caffeine was real and could not be
explained away by different rates of morning sickness.
Dr. Carolyn Westhoff, a professor of obstetrics and gynecology,
and epidemiology, at Columbia University Medical Center in New York,
had reservations about the study, noting that miscarriage is
difficult to study or explain.
She said most miscarriages resulted from chromosomal
abnormalities, and there was no evidence that caffeine could cause
those problems.
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