Dr. Li によれば、1063人の妊婦の調査で、172人16%が流産した。カフェインを全くとらない264人中12.5%が流産したが、１日200mg以上摂取した164人中では24.5%であった。
Study Sees Caffeine Possibly Tied to Miscarriages
By DENISE GRADY
Published: January 20, 2008
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, although the subject has long been contentious, with conflicting studies, fuzzy data and various recommendations given over the years.
The new study, to be 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.
Pregnant women should try to give up caffeine for at least the first three or four 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, Calif.
“If, for whatever reason, they really can’t do it, think of cutting to one cup or switching to decaf,” Dr. 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.
“Women do need good guidance,” she said.
Dr. 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.
Dr. Li said the study 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.
Dr. Li said he and his colleagues 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 of epidemiology, at Columbia University Medical Center, had reservations about the study, noting that miscarriage is difficult to study or explain. She said that most miscarriages resulted from chromosomal abnormalities, and that there was no evidence that caffeine could cause those problems.
“Just interviewing women, over half of whom had already had their miscarriage, does not strike me as the best way to get at the real scientific question here,” she said. “But it is an excellent way to scare women.”
She said that smoking, chlamydial infections and increasing maternal age were stronger risk factors for miscarriage, and ones that women could do something about.
“Moderation in all things is still an excellent rule,” Dr. Westhoff said. “I think we tend to go overboard on saying expose your body to zero anything when pregnant. The human race wouldn’t have succeeded if the early pregnancy was so vulnerable to a little bit of anything. We’re more robust than that.”
Last Updated: Monday, 21 January 2008, 05:06 GMT
Coffee 'raises miscarriage risk'
Caffeine content can vary with brands and brewing methods
Pregnant women should consider avoiding caffeine say researchers who found even moderate consumption in early pregnancy raises the risk of miscarriage.
Currently, the Food Standards Agency sets an upper limit during pregnancy of 300mg - or four cups of coffee a day.
But a US study in the American Journal of Obstetrics and Gynaecology found 200mg of caffeine a day doubled the risk compared to women who abstained.
Experts said they would review the data to see if advice needed changing.
Women probably should consider stopping caffeine consumption during pregnancy
Study author Dr Li
Pat O'Brien, consultant obstetrician and spokesman for the Royal College of Obstetricians and Gynaecologists, said based on the findings he would now be advising women in their first 12 weeks of pregnancy to abstain from caffeine altogether.
"The first 12 weeks is a very vulnerable time for the baby. It's when most miscarriages occur," he explained.
He said most women in early pregnancy went off the taste of caffeinated drinks anyway and so should not find abstaining from them too difficult.
But he said it was unclear whether pregnant women needed to avoid caffeine in later pregnancy.
An estimated one in five pregnancies in the UK will end in miscarriage, affecting around 250,000 women in the UK every year.
There are a number of well-established risk factors, such as increased maternal age, a previous history of miscarriage, and infertility.
But the causes of the majority of miscarriages are not fully understood.
Caffeine has been mooted as a risk factor before, but studies have yielded conflicting results.
For the latest research, Dr De-Kun Li and colleagues at the Kaiser Permanente Division of Research, studied 1,063 women who had become pregnant in the last month or two.
300 mg of caffeine is roughly equivalent to:
Four average cups or three average mugs of instant coffee
Three average cups of brewed coffee
Six average cups of tea
Eight cans of regular cola drinks
Four cans of so-called "energy" drinks
400g (eight standard 50g bars) of normal chocolate
Caffeine content in a cup of tea or coffee varies by different brands and brewing methods
Source: Food Standards Agency
They asked the women to provide a detailed diary about their caffeine intake up to their 20th week of pregnancy.
When they compared this information with how many of the women had miscarried by 20 weeks gestation, 172 of the women in total, they found a link.
Compared with non-users, women who consumed up to 200mg of caffeine a day had an increased risk of miscarriage - 15% versus 12%.
For women who drank more than 200mg, the risk increased to 25%.
The increased risk appeared to be related to the caffeine itself, rather than other coffee ingredients because other caffeinated beverages such as tea and hot chocolate showed a similar trend to coffee.
Caffeine is able to cross the placenta to the foetus, but it is not clear what affect this has on the growing baby.
Dr Li said: "The main message for pregnant women from these findings is that they probably should consider stopping caffeine consumption during pregnancy."
Zoe Wheeldon from the British Coffee Association said the latest research, although well designed and robust, did not change the current Food Standards Agency recommendation of a safe upper limit of 300mg of caffeine per day for pregnant women.
"This evidence must be reviewed in conjunction with existing research and it is important to review all the available data rather than taking one study in isolation."
A spokesman from the Food Standards Agency said: "In order to provide a more robust basis for the FSA's advice to pregnant women on caffeine consumption, an FSA-funded study, involving around 2,500 pregnant women, was commissioned in 2003.
"This is almost complete and the results will be presented to the Committee On Toxicity in closed session for consideration.
"We will ask the committee to also look at this new American study. When the committee has reached conclusions the agency will, if appropriate, revise its advice on caffeine consumption in pregnancy."
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