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A researcher has been trying to nail down more specific facts behind a common piece of medical advice. The advice goes to expectant mothers. Doctors often tell them to limit caffeine during pregnancy. The question for researcher DeKoon Lee(ph) and a team of researchers funded by Kaiser Permanente in California was how much is too much? The researchers found that just one or two cups of coffee per day can increase the risk of miscarriage. And we have more this morning from NPR's Allison Aubrey.
ALLISON AUBREY: The study included about a thousand women from the San Francisco Bay region. And what's unique is that researchers had the women write down exactly how much coffee, tea and caffeinated sodas they were drinking, starting in the earliest weeks of their pregnancy.
Ms. TRACY FLANAGAN (Kaiser Permanente): They were recruited early in pregnancy from a pregnancy test.
AUBREY: Tracy Flanagan is director of Women's Health at Kaiser Permanente's Northern California region. She explains most of the women were in their late 20s to mid-30s, and at the end of the study researchers took their caffeine diaries and put them in one of three groups, those who drink no caffeine, those who consumed just a little, and those who drink moderate amounts, 200 milligrams or more per day. It turned out that those in the last group double their risk of miscarriage compared to women who drink no caffeine.
Ms. FLANAGAN: To me what's really interesting about the study is that so many causes of miscarriage are not alterable by lifestyle or by anything a woman can do. So cutting out caffeine can be a pretty easy thing to do for three or four months in the early part of pregnancy when miscarriage rate is the highest.
AUBREY: Flanagan says many studies have found a link between high caffeine intake and miscarriages. But this study evaluated the risk of just 200 milligrams or more of caffeine per day.
Looking at the findings, Flanagan says it can be tricky to translate them into easy advice for women. If you stick to the idea of limiting consumption to just one caffeinated drink a day, it does not take into account all the variation in caffeine concentration and serving sizes too.
Take, for instance, a standard cup of auto-drip coffee. An eight-ounce mug will have roughly 140 milligrams of caffeine. But how many people pay attention to how many ounces they're drinking?
Ms. FLANAGAN: Most people don't actually measure out a measuring cup of coffee. How it's brewed makes a difference.
AUBREY: As do the beans, and where you might buy your coffee. If your morning starts with a stop at Starbucks, one tall coffee has more than 200 milligrams. For women who want to taper down caffeine, green tea is one option. Green tea typically has just about 25 milligrams per cup. That's one-tenth of the tall coffee.
Regular tea has a little more and diet sodas are in the same ballpark. Drinking one of these a day is a way to stay below the 200 milligram threshold. The other option for pregnant women or those trying to become pregnant is just to go cold turkey. That's what 35-year-old Tammy Plotkin-Oren did despite her love of the morning ritual.
Ms. TAMMY PLOTKIN-OREN: I definitely miss it, you know, when we'd sit around with a group of friends and I was the only one who is pregnant and everyone's, you know, drinking a hot cup of coffee.
AUBREY: But she says switching to herbal tea was the obvious choice. She explains her first pregnancy did end in a miscarriage.
Ms. PLOTKIN-OREN: I remember asking a lot of questions about like, is it something that I did? How can I - what can I do differently so that it doesn't happen again?
AUBREY: She had already cut out alcohol and was not a smoker, so eliminating caffeine was the change she could make.
Ms. PLOTKIN-OREN: I think I'd really made the decision that I was going to do anything that I had control over. So it was very black and white to me. It was like, okay, no more caffeine, we're done.
AUBREY: Three healthy children later, she says clearly giving caffeine up wasn't much of a sacrifice.
Allison Aubrey, NPR News, Washington.
INSKEEP: You can find out how much caffeine is in certain drinks and food at npr.org.