Watch CBSN Live

Too Much Caffeine Increases the Risk of Miscarriage

Today's New England Journal of Medicine has a study that links caffeine to the risk of miscarriage in pregnant women. Dr. Bernadine Healy tells us more about the findings.

For years, obstetricians and prenatal healthcare providers have suspected a connection between caffeine and miscarriage, so they advised pregnant women to limit their caffeine intake. A new study in the New England Journal of Medicine reveals that five cups of coffee per day more than DOUBLES a pregnant woman's chance of having a miscarriage.

In the meantime, the US Food and Drug Administration and the March of Dimes, which funds research on birth defects, have both advised pregnant women to curtail caffeine. Caffeine, which is easily passed to the fetus, stays in the body longer among pregnant women.

Unlike earlier research, the latest study looked at women in the first trimester, when most miscarriages occur. It also tried to account for a separate risk from genetic defects in fetuses and a possible risk from smoking.

The More You Drink, The Greater The Risk

The research team in Sweden and the United States found that the equivalent of one-to-three cups of American coffee increases the risk of miscarriage by 30%. Three to five cups raises the risk by 40%. Five cups or more yields more than doubled the risk.

Not All Coffee Are Created Equal

The findings are based on interviews with 562 women who had miscarriages between six to 12 weeks of pregnancy (the first trimester), and 953 pregnant women who did not. Since they were Swedish, they often drank stronger coffee than Americans did. The results are "translated" to American cups of coffee.

A cup of Swedish coffee typically carries about 180 milligrams ("mg") of caffeine, compared to the 100 mg in a typical American cup of coffee.

Smokers May Not Have Increased Risk

Interestingly, among nonsmokers, more miscarriages occurred in women who drank at least 100mg per day. Among smokers, caffeine was NOT associated with increased risk of abortion. The researchers say this is probably because the smokers already face a higher risk of miscarriage.

Two Cups Still Okay

Dr. Sven Cnattingius of the Karolinska Institute in Stockholm directed the study. He suggests that pregnant women curtail their coffee to the equivalent of about two American cups per day.

Caffiene In Drinks & Medicine

Tea, cocoa and coke normally contain less caffeine per ounce than coffee. But the study suggests a similar effect on miscarriage for these drinks and for medications with caffeine, if enough is consumed. Caffeine is also present in chocolate.

On The Other Hand: The Morning Sickness Effect

The researchers also tried to account for the effects of morning sickness, which tended to exaggerate the impact of caffeine in earlier studies because nausea is more common in pregnant women with healty fetuses. Since morning sickness gives many women with healthy fetuses a distaste of coffee, more unhealthy fetuses are found among coffee drinkers.

Dr. Mark Klebanoff, at the National Institute of Child Health and Human Development, who was familiar with the findings, said it is still possible that morning sickness skews the results. "I think it will never be completely possible to rule it out, no matter how good a study you do," he said. But Klebanoff said this study is probably the strongest yet, because it was specifically designed to answer whether caffeine promotes miscarriage. Other studies used data initially collected to resolve other questions.

Coffee Industry Objects

Robert Nelson, president of the New York-based National Coffee Association trade group, argued that research indicates pregnant women can drink perhaps up to four cups of coffee a day without apparent risk. He believes, like Klebanoff, that studies tie coffee to miscarriage because woen with healthy pregnancies tend to develop an aversion for coffee and other drinks with strong aromas.

"The body of evidence after decades, including this study, confirms the fact that coffee can be consumed safely in moderate quantities in pregnant women," he said.

Interview With Dr. Bernadine Healy

What's new and interesting about the findings?

What makes this study new and interesting is that it focuses on non-smoking women. And it looks at (fetuses) with healthy genes. I think the risk of spontaneous abortion in normal gene fetuses was studied. Most are related to abnormal chromosomes. What they showed here is that X-percent occurs in babies that have no other abnormality. They appeared normal genetically, so there was no other obvious cause of the miscarriage. It is a stronger argument for a link because they identified it among fetuses with normal chromosomes.

The more you drink the greater the risk. Does this mean coffee drinkers have to go "cold turkey" if they get pregnant?

I would say coffee drinkers should limit their intake to no more than one cup per day. Not just when pregnant but before pregnancy occurs. Other studies show coffee also decreases your chances of getting pregnant. It makes you less fertile, and when you become pregnant it makes you less able to carry the baby. And it's also associated with low birth-weight babies. Women who plan to become pregnant should limit themselves to one cup of coffee a day.

Why are smokers NOT more likely to have miscarriages if they drank coffee?

There are three major environmental toxins that can harm a pregnancy: smoking, alcohol and coffee. We know that smoking endangers pregnancies. We know alcohol is another. Coffee is more controversial, the studies are less clear. But this study shows that coffee is as risky as cigarette use - it's in the league of smoking. This doesn't mean that if you smoke you can drink coffee or alcohol--it means you shouldn't do ANY of them

Probably because smoking has an adverse effect on the baby that is present throughout the pregnancy. It's associated with miscarriage, low birth-weight babies, damaged placentas... so the damage has already been done. Adding coffee to it doesn't make it particularly worse. Smoking is an absolute no-no during pregnancy. No woman who wants a healthy pregnancy should smoke, but she can consume some coffee.

Does caffeine in non-coffee drinks or food pose danger to pregnant women?

Yes. Not with one candy bar. But you cannot eat four pounds of chocolate. A cup of tea is safe.

How can you tell if medicine has caffeine in it?

Read the labels! It's in "headache powders" like Excedrin... and some migraine medicines. No woman who's pregnant should be taking migraine medicines.

How did morning sickness skew the study a little?

When women have morning sickness they are less apt to have problems with spontaneous abortions. One of the theories is that the nausea protects them from environmental toxins--they get food aversions. They are less likely to drink coffee.

How much coffee is safe?

If you look at the study, it suggests a woman should not exceed a cup of coffee a day. That may be conservative, but it makes sense and I agree with it.

Why is the difference between Swedish and American coffees important?

Coffee around the world comes in different concentrations. The Swedish coffee was nearly twice as strong as American coffee. Like cappuccino or Turkish coffee, which must have three thousand mg of caffeine!

©MMII CBS Worldwide Inc. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed

View CBS News In
CBS News App Open
Chrome Safari Continue