Drinking a couple of cups of coffee a day has long been considered safe during pregnancy, but a new study finds that even this modest amount of caffeine could double a woman’s risk of miscarriage.
Doctors are split on what this means for pregnant women, with some advising avoiding caffeine altogether and others saying buzz-inducing beverages are still safe in moderation.
Previous studies have linked caffeine to an increased risk of miscarriage, but they have focused on higher doses and the connection has been controversial, with some experts arguing that the research didn't account for morning sickness. The nausea and vomiting of morning sickness, caused by elevated hormones, is generally a sign of a reduced risk of miscarriage — and also can lead women to stop drinking their usual coffee or other caffeinated drinks. The concern was that the cutback in caffeine among these women could make it appear caffeine was associated with miscarriage
To get to the bottom of this puzzle, a team led by Dr. De-Kun Li, a researcher at Kaiser Permanente in Oakland, Calif., conducted one of the first studies to take into account morning sickness. They concluded that a daily habit of drinking 200 milligrams of caffeine — the amount typically found in just two cups of coffee — significantly increases the risk of miscarriage.
“If women become pregnant or are actively planning to become pregnant they should probably think about stopping drinking caffeine, at least during the first trimester when most miscarriages occur,” Li said.
“If they really have to drink, they should probably limit it to one cup of coffee per day,” he added.
Coffee, tea and soda pose same risks
The source of caffeine — whether from coffee, tea or sodas — didn't make a difference. But one thing to take into consideration is that a cup of coffee can have varying amounts of caffeine depending on how it is brewed, with some brands containing more of the addictive chemical than others. A tall brewed coffee from Starbucks, for instance, packs 270 mg of caffeine. A tall latte from the chain, however, contains 75 mg.
In the study, published in Monday’s issue of the American Journal of Obstetrics and Gynecology, Li's team interviewed 1,063 women in the San Francisco area who became pregnant between 1996 and 1998 about their caffeine intake. While 164 of the women drank 200 mg of caffeine or more daily, 635 consumed some caffeine but less than 200 mg. The remaining 264 women said they didn’t consume any caffeine.
Overall, 172 of the women suffered a miscarriage. The risk of a miscarriage was more than double in women who consumed 200 mg or more of caffeine, with 25 percent suffering a miscarriage compared to just 12 percent of women who didn't consume caffeine. The low-caffeine drinkers also appeared to have an elevated risk of miscarriage, but this trend wasn't statistically significant, meaning the researchers could not rule out that it was merely due to chance.
2-cup cutoff point
Li said the 200 mg limit can be considered a cutoff point where the miscarriage risk starts to emerge because the median consumption of the high caffeine intake group was 301 mg per day. This means half of these women were drinking less than 301 mg daily, so heavy drinkers were probably not skewing the results.
To determine the impact of morning sickness on the results, Li's team looked separately at women who experienced nausea and vomiting and those who did not. The miscarriage risk remained in both groups as long as their daily caffeine intake rose above 200 mg. In addition, the researchers looked at women who reduced their caffeine consumption during their pregnancy and those that didn’t and found that the miscarriage risk still remained in those consuming 200 mg or more of caffeine per day.
The increased risk remained even after adjusting for other factors that could up the chances of a miscarriage, such as age, previous miscarriage, smoking and alcohol consumption.
Although it's not known for certain how caffeine might trigger a miscarriage, one theory is that it restricts blood flow to the placenta, which could have a detrimental effect on the developing fetus, Li said.
Overall though, caffeine is not a major cause of miscarriage, which occurs in up to 20 percent of known pregnancies. More than 60 percent of these faulty pregnancies are due to chromosomal defects in the fetus that are beyond the mother's control.
Doctors on the frontlines are divided on the risks of caffeine. Dr. Tracy Flanagan, an obstetrician/gynecologist and director of women's health for Northern California at Kaiser Permanente, said that based on the study findings, she will be more emphatic about advising her pregnant patients to cut back on coffee and other caffeinated beverages.
Flanagan said that along with other prenatal advice, such as taking folic acid supplements, no alcohol and no smoking, she would add limiting caffeine intake to no more than the amount in one cup of coffee per day or to cut it out entirely.
But Dr. Katharine O'Connell, a gynecologist at Columbia University, remains unconvinced. She said the study would not be enough to change her advice to patients and doubted it would overturn current recommendations from the American College of Obstetricians and Gynecologists that moderate caffeine intake during pregnancy is safe (ACOG said it does not comment on individual studies).
“I would tell my patients that two cups of coffee per day should be fine,” O'Connell said.
She noted however that the findings were intriguing because previous studies that have linked caffeine to an increased risk of miscarriage involved much higher amounts — the equivalent to several cups of coffee per day. But the current study suggests the risks begin at a lower amount, so this may warrant further investigation, she said.
Too early for alarm
It's too early to sound the alarm though, according to O'Connell. Larger studies that confirm the miscarriage risk would be necessary before these relatively low amounts of caffeine are considered unhealthy, she said.
Without a final word on the matter, moms-to-be are likely to hear conflicting advice from their doctors and simply decide on their own whether lattes are worth even the slightest chance of a risk.
Tammy Plotkin-Oren, a coffee-lover and mother of three daughters in San Francisco, said giving up java while pregnant is doable and she should know. After her first attempt at pregnancy seven years ago ended in miscarriage, Plotkin-Oren, 35, went cold turkey during subsequent pregnancies.
Although there's no way to know if her 3 to 4 cups of coffee habit per day played a role in the miscarriage, she said she decided to eliminate her intake during her next three pregnancies as part of her overall health plan and each one resulted in a successful birth.
Plotkin-Oren missed the social aspect of meeting friends for coffee and developed headaches from caffeine withdrawal, but overall she found it easy to kick the habit. “It wasn't that hard because I was committed to doing everything I could to ensure a successful pregnancy,” she said.
Steve Mitchell is a science and medicine writer in Washington, D.C. His articles have appeared in a variety of newspapers, magazines and Web sites, including UPI, Reuters Health, The Scientist and WebMD.