Study: Caffeine raises miscarriage rate

January 21, 2008 12:26:58 PM PST
Expectant mothers have been confused for years about whether drinking that morning cup of joe could do harm to their unborn child. Some previous studies have shown that consuming caffeine during pregnancy increases a woman's risk for miscarriage, while others have found that drinking just a couple cups of coffee a day doesn't pose much of a threat.

The latest research to examine the risk of caffeine consumption during pregnancy reveals that women who said they drank more than two cups of coffee per day had nearly double the risk of miscarriage compared with women who consumed no caffeine.

Researchers at the Kaiser Permanente Research Division in Oakland, Calif., followed 1,063 women during their pregnancy and asked about their caffeine intake. From October 1996 to October 1998, researchers examined the effects of the stimulant among the women who said they never decreased their caffeine consumption during their pregnancy.

They found that women who consumed 200 milligrams or more of caffeine daily the equivalent of two or more cups of coffee or five 12-ounce cans of soda -- had twice the risk for miscarriage. Moreover, the study found that even those women who consumed less than 200 milligrams of caffeine daily had about 40 percent increased risk for miscarriage.

Coffee: 'Toxic Stuff'

"I am not at all surprised by this study," said Dr. Sherman Silber, director of the Infertility Center at St. Lukes Hospital in St. Louis. "Coffee is toxic stuff."

But does this study carry enough weight to finally answer the question of whether pregnant women should give up caffeine altogether?

Dr. De-Kun Li, primary study investigator, said that he hopes the research will convince doctors to tell their pregnant patients to avoid coffee completely.

"This is something you can control if you're worried about a miscarriage," Li said. "There's lots of things we can't control, but this is one thing that you can."

However, Li admitted that the study fails to answer the question of whether small amounts of caffeine significantly increase a woman's chance for miscarriage.

"Is this study going to make doctors firmly give a cutoff point for how much caffeine is safe for a pregnant woman to consume? I think that controversy will remain," Li said. "From our study, we can probably say that consuming above 200 milligrams of caffeine is not safe, but below that we can't say definitively if it is or isn't."

Previous research examining the effects of caffeine consumption during pregnancy has looked at how the stimulant might pose harm to the fetus, but offered no information on whether drinking just one or two cups of coffee a day still poses a significant risk.

What is known is that caffeine is a stimulant that increases alertness, blood pressure, heart rate and urine production. Some doctors believe that pregnant women may be especially sensitive to it because it takes them longer to digest and clear the stimulant from their body.

Moreover, the unpleasant side effects of caffeine on the expecting mother -- such as anxiety, indigestion and trouble sleeping -- may be equally unpleasant for the baby.

During pregnancy, caffeine crosses the placenta and reaches the fetus. According to a 2001 fact sheet on caffeine and pregnancy by the Organization of Teratology Information Services, caffeine increases the fetal heart rate and breathing rate just as it does the mother.

Conflicting Evidence

More recently, a study published in the American Journal of Epidemiology in 2003 suggested that large amounts of caffeine consumption may slightly reduce a baby's birth weight.

But it seems that an equal amount of conflicting evidence on the effects of caffeine during pregnancy has surfaced in the last few years.

A study published in the journal Epidemiology earlier this month revealed that pregnant women who drank moderate amounts of coffee -- that is, less than two cups of coffee a day -- did not have an increased risk for miscarriage compared to women who drank no caffeine during pregnancy.

But this latest research on caffeine and pregnancy is confirmatory of previous studies, which also linked caffeine consumption to increased risk for miscarriage. However, many doctors have remained skeptical of studies drawing a definitive link between moderate caffeine consumption and an increased risk for miscarriage.

Although there's a fairly large number of epidemiological studies over the last 10 years suggesting that large amounts of caffeine consumption increases a woman's risk of miscarriage, many experts remain unconvinced of these study's conclusions.

According to Dr. Richard Paulson, chief of the Division of Reproductive Endocrinology and Infertility at the University of Southern California, such epidemiologic studies fail to control for many of the mother's behaviors which could be potentially harmful to the fetus and uterine environment.

"Those [women] who drink caffeine also take worse care of themselves," Paulson explained. "Even if you 'control' for those things, you can't control for other behaviors."

The study attempted to control for potentially harmful behaviors by identifying those women who smoked or consumed alcohol during their pregnancy. But the study also revealed that women who consumed large amounts of caffeine during their pregnancy were also more likely to consume alcohol; about 55 percent of women in the high caffeine group said they drank alcohol while they were pregnant, compared to about 29 percent of women in the group who drank no caffeine during pregnancy.

Genetic Factors

Because women who consume caffeine during pregnancy are also more likely to smoke and consume alcohol during pregnancy, many doctors say that this study fails to offer conclusive evidence on whether a miscarriage was caused by caffeine or another toxin.

The study also failed to identify whether genetic factors were to blame for some of the participants' miscarriages.

"The coup de grace is that they did not look at whether or not the miscarriages were normal chromosomally, meaning that they were caused by some sort of 'toxin,'" explained Paulson.

However, Li said that because his team controlled for women who experienced nausea and morning sickness during pregnancy, it was able to get a more accurate reading on the link between caffeine and miscarriage.

"Critics argue that the reason we saw this association was not so much because caffeine increases risk for miscarriage but because healthier women are more likely to experience morning sickness, and therefore also more likely not to drink coffee since they're feeling nauseous," Li said.

"We went one step further than just controlling for this -- we looked closely at the group of women that didn't change their caffeine consumption at all from before their pregnancy."

But Dr. Tommaso Falcone, professor and chair of the Department of Obstetrics & Gynecology at the Cleveland Clinic, said that an important factor to consider when analyzing this study is that 130 of the 172 total miscarriages for the entire group of participants occurred in the group of women who consumed either no caffeine or under 200 mg of caffeine per day.

"[This means] that miscarriages can still occur and women should not feel that they caused it by having a cup of coffee," Falcone said.

Still, the general recommendation of doctors is that pregnant women significantly cut back on their caffeine intake, if not give up the stimulant entirely.

"Nonetheless, I think it is good enough to make our recommendation that women should abstain from caffeinated beverages," Falcone added.


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