2-cup coffee habit may double miscarriage risk

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.