New research warning expectant mothers against drinking too much coffee during pregnancy is adding further fuel to the heated debate over the role caffeine plays in a woman's risk of miscarriage.
Pregnant women who consume more than 200 milligrams of caffeine, or more than two regular cups of coffee, on a daily basis are twice as likely to suffer a miscarriage as those who consume none, according to a study by the Kaiser Permanente Division of Research.
The researchers interviewed 1,063 women and found that 12.5 per cent of participants who reported no caffeine intake suffered miscarriages, compared with 25.5 per cent of women who said they consumed more than 200 milligrams a day.
While coffee was the major source of caffeine for a majority of women involved in the study, some drank tea or caffeinated soda, leading researchers to conclude that caffeine, and not other chemicals in coffee, was the common factor linked to a higher miscarriage risk.
The finding, published today in the American Journal of Obstetrics and Gynecology, is the latest piece of evidence being used to support the view that pregnant women who drink a few cups of coffee a day may be asking for trouble.
In light of the risks, "it may be prudent to stop or reduce caffeine intake during pregnancy," concludes the study by Kaiser Permanente, a private health-care provider in California.
It's a belief that has created division in recent years between physicians who see caffeine as a risk and those who think potential dangers are being exaggerated.
"I think the point about pregnancy in general is the precautionary principle makes sense, but there's a difference between caution and hysteria," said Gideon Koren, director of the Motherisk Program at Toronto's Hospital for Sick Children.
While he doesn't dispute the link between high caffeine levels and an increase in miscarriage risk, he said the potential danger may be blown out of proportion and fail to take other risk factors into account.
Dr. Koren said he advises pregnant women to limit their caffeine consumption to 150 milligrams a day, or less than two regular cups.
However, expectant mothers shouldn't be scared into thinking that exceeding those guidelines will automatically put their babies at serious risk, he said.
Although numerous studies have demonstrated a link between high doses of caffeine and a greater chance of miscarriage, there are many factors at play that could contribute to that outcome.
For instance, women who are heavy coffee drinkers are often much more likely to smoke as well, which could contribute to the risk of miscarriage. Other factors, such as a woman's alcohol consumption or previous history of miscarriage, could increase her chances of problems during pregnancy.
"This whole area of research is very difficult," Dr. Koren said.
In the new Kaiser study, researchers attempted to take those variables into account by asking participants about their behaviour and background, and whether they experienced any nausea or morning sickness.
Even after controlling for factors that could contribute to the likelihood of miscarriage, researchers found women who consumed more than 200 milligrams of caffeine a day were at a higher risk.
But the study doesn't specify how much caffeine was consumed by those who reported having more than 200 milligrams a day. That distinction is important because some women could have been consuming extremely high levels.
In total, one-quarter of survey participants said they had no caffeine intake during pregnancy; 60 per cent reported consuming between zero and 200 milligrams a day, and 15 per cent said they exceeded 200 milligrams a day.
About 16 per cent of survey participants suffered miscarriages.
Dr. Koren said some medical studies seem to overstate possible risks by linking moderate caffeine consumption with higher miscarriage rates.
The basic message pregnant women should keep in mind is that caffeine should be consumed in moderation, he said.