In the age of Starbucks venti lattes, it's tough for expectant moms to go cold turkey on caffeine. But they may want to cut back because of the possibility that the popular stimulant increases the risk of miscarriage.
A study published Monday in the American Journal of Obstetrics and Gynecology (AJOG) reports that women who reported consuming more than 200 milligrams of caffeine a day during the first three months of pregnancy doubled their risk of miscarriage (from the 12 percent average among participants who used no caffeine to 25 percent). During a two-year period, 1,063 pregnant San Francisco-area women participated in the study.
Traditionally, groups like the American College of Obstetricians and Gynecologists and the March of Dimes have told women that drinking one or two cups of coffee a day is OK for most pregnant women. But these new findings suggest otherwise. Indeed, expectant mothers might be surprised to find out how little 200 mg of caffeine is by today's mega-cup standards. For example, the smallest size of Starbucks' regular coffee, the "tall" or 12-ounce cup of brewed joe, has 260 mg of caffeine. An eight-ounce cup of regular drip coffee contains 137 mg, an eight-ounce cup of brewed tea contains 48 mg and a 12-ounce soda contains about 37 mg.
Exactly how caffeine might be affecting the developing fetus is unclear. Doctors know that that the stimulant can easily cross the placental barrier to the fetus, but whether there's a negative impact, is unclear. "That's true of most things that cause miscarriage," says Dr. Mark Nichols, an OB/GYN at Oregon Health and Sciences University.
It could be because caffeine constricts the blood vessels and restricts blood flow to the placenta, says De-Kun Li, co-author of the new study and a researcher in the division of research at Kaiser Permanente in northern California. Or it could be that caffeine interferes with developing cells' normal function. "The fetus is very sensitive to any environmental insult," says Li. Even with the ambiguity, the findings are enough to convince Li. "If it was my wife, I would say stop drinking for [the first] three months [of pregnancy]," he says.
Still, research on the link between caffeine consumption and miscarriage remains controversial. Also this month, in the journal Epidemiology, researchers reported that consuming less than about two cups of coffee a day was unrelated to miscarriage. "I am not persuaded [caffeine] poses a health hazard. We really don't know the truth," says epidemiologist David Savitz, professor of community and preventive medicine at Mount Sinai School of Medicine in New York and co-author of the Epidemiology study.
Savitz considers caffeine "among the long list of things you should think about," but it's not like smoking or heavy alcohol consumption where the medical recommendations are unambiguously discouraging. He notes that most women in their first trimester, when the miscarriage risk is highest, naturally cut back substantially on caffeine either because of nausea or health concerns.
Yale University OB/GYN Mary Jane Minkin, author of "The Yale Guide to Women's Reproductive Health," already tells her patients to limit caffeine consumption in part because it helps prevent breast discomfort. But she also wants women to understand that miscarriage is most often related to chromosomal abnormalities, not to caffeine. "Far and away, the most common cause of miscarriage is that that sperm and that egg didn't get together so well," she says. "Somehow in the chromosomes, things aren't looking so terrific." It's not because of anything the mom did. "Even if you move to Idaho and breathe fresh air and drink fresh milk, even there you're still going to have a baseline miscarriage rate of about 15 percent," she says.
One other thing to note is that the AJOG study linking caffeine and miscarriage was an "observational" trial, not a prospective, double-blind controlled trial that injected some women with caffeine and others with none. It relied on the self-reports of pregnant women who were members of a Kaiser Permanente health care program in northern California. "What people report to you they've done isn't necessarily what they've done," says Dr. Alan Peaceman, professor of Obstetrics and Gynecology at Northwestern University's Feinberg School of Medicine and an expert in high-risk pregnancy.
Peaceman notes that some women develop "terrible headaches" without their coffee. And he wants to avoid "creating hysteria here." "I tell women not to be guilty about a cup of coffee a day if that's really what they need," he says. "There are a lot of people who are hooked on caffeine, including myself. Some women, if they don't have it, have nausea and vomiting, and then their nutritional status diminishes. I'd rather have them have a cup of coffee. There is so much guilt out there that women have to deal with when they have a bad outcome in pregnancy. The vast majority is not within their control." But he also wants women to consume as little as they can get away with just in case. "When I tell a woman she can have a cup of coffee, I'm not talking about a double espresso venti," he says. "I'm talking about a regular, eight-ounce coffee."
Given the inconclusive evidence, what's a pregnant latte lover to do? "Women are always asking what they can do to improve the health of their baby. There are so many things they can't control," says OB/GYN Tracy Flanagan, director of women's health for Kaiser Permanente in northern California. "That's not to say cutting out coffee is going to prevent miscarriage. What it can do is decrease the chance." She plans to add caffeine to her list of issues she discusses with women, including folic acid, prenatal vitamins, smoking and alcohol. If women want a healthy, alternative stimulant, they can exercise, she suggests. And why not try decaf coffee or tea, or even apple cider?