Caffeine increases miscarriage risk
Publication Date:18/01/2008
Pregnant women may want to cut down the amount of caffeine they take in through caffeinated drinks, after research has showed just two cups of coffee a day may increase the risk of miscarriage.
What do we know already?
Miscarriage in the first 12 weeks of pregnancy is quite common. It happens to about 1 in 6 pregnant women. Mostly, we don't know the reason why. It's likely to be because the baby is not developing properly.
Drinking coffee has been linked to a higher risk of miscarriage before, but researchers weren't sure that caffeine was really the cause. They thought the link might be because women who had morning sickness (nausea and vomiting in pregnancy) were less likely to feel like drinking coffee. Women who have morning sickness are generally at less risk of miscarrying.
Even so, pregnant women have been advised to restrict the amount of caffeine they drink, because of the possible risk.
The new study looks at the risk of miscarriage and caffeine from tea, coffee and soft drinks (such as cola). It also takes account of other factors like morning sickness.
What does the new study say?
The study showed that that drinking even moderate amounts of caffeine seems to increase the risk of miscarriage. It found that women who drank more than 200 mg of caffeine (the equivalent of about 2 cups of ground coffee) were twice as likely to miscarry, compared to women who drank no caffeinated drinks at all.
Tell me more about the study's findings
Just over 1000 pregnant women took part in the study. They were recruited into the study as soon as they had a positive pregnancy test. Of these women, 16 in every 100 had a miscarriage during the first 20 weeks of their pregnancy.
When the researchers compared the women who'd had a miscarriage with the women who had not, the women who miscarried were more likely to have been drinking some caffeine. The risk was greatest for those who had 200 mg or more.
- 12 in 100 women who drank no caffeine at all had a miscarriage
- 15 in 100 women who drank less than 200 mg of caffeine daily had a miscarriage
- 25 in 100 women who drank more than 200 mg of caffeine daily had a miscarriage
The increased risk stayed about the same when researchers looked separately at women who had felt sick or vomited during their pregnancies, and women who had no morning sickness. So the researchers think it's likely that caffeine really does increase the risk of miscarriage.
Where does the study come from?
The study was carried out by researchers from a big health insurance company in the US called Kaiser Permanente. It was published in the American Journal of Obstetrics and Gynecology, which is owned by a publishing company called Elsevier.
How reliable are the findings?
This type of study cannot prove for certain that caffeine caused the increased numbers of miscarriages of the women who drank caffeine. However, the study does show that caffeine seems to be the most likely cause.
The researchers were very careful to take account of all the other factors that we know can affect the risk of miscarriage, such as the woman's age, previous miscarriages, morning sickness, smoking and alcohol use.
However, the researchers weren't able to test how much caffeine the women actually drank. They relied on the women's reports of what they drank, and assumed average amounts of caffeine for each drink of tea, coffee and cola. So the results are based on estimates of how much caffeine the women consumed.
What does this mean for me?
This research is important for women who are pregnant or trying for a baby. Sadly, there's nothing you can do to guarantee you won't have a miscarriage. It happens to lots of people, including women who don't drink any caffeine. Don't feel guilty if you've had a miscarriage in the past, and drank coffee during pregnancy. The research about caffeine hasn't been very clear up until now.
However, it makes sense to think about restricting or giving up caffeine now that the research is clearer. It's a good idea to know how much caffeine you take in through drinks. A survey carried out by the Food Standards Agency in the UK found that:
- One cup of tea of average size and strength had 40 mg caffeine
- One cup of instant coffee of average size and strength had 54 mg caffeine
- One cup of ground coffee of average size and strength had 105 mg caffeine.
The size and strength of the drinks varied quite a lot. Weaker, smaller servings had much less caffeine than stronger, larger servings.
The Food Standards Agency advice is that women shouldn't drink more than 300 mg (about three cups of ground coffee) a day. But this new research suggests restricting yourself to just one caffeinated drink a day, or cutting out caffeine altogether.
What should I do now?
If you're pregnant, think about the amount of caffeine you take in daily, using the figures above as a guide. If you drink 200 mg or more daily, it may be best to consider cutting down to just a small amount, or giving up altogether. You could try alternatives such as fruit teas, or decaffeinated versions of tea and coffee.
From:
Weng X, Odouli R, Li DK. Maternal caffeine consumption during pregnancy and the risk of miscarriage: a prospective cohort study. American Journal of Obstetrics and Gynecology. Published online January 2008.
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