A study was recently published in the European Journal of Obstetrics & Gynecology and Reproductive Biology entitled ‘Associations between consumption of coffee and caffeinated soft drinks and late stillbirth—Findings from the Midland and North of England stillbirth case-control study’.
The media were quick to jump in with headlines such as ‘Just one cup of coffee a day during pregnancy may raise the risk of stillbirth’.
Really? Is coffee that dangerous?
Not on an individual level no. After seeing this article, muttering a lot and sending several exasperated emails about the way this study was publicised and the anxiety it could cause pregnant women, we – this is Amy Brown and Sara Wickham – thought we’d point out the differences between the headlines and what the study actually looked like and hopefully put minds at rest.
Sounding familiar yet?
The study was yet another study looking at caffeine intake during pregnancy and outcomes such as stillbirth. For some reason, researchers really seem to like looking at caffeine and pregnancy lately and seem determined to terrify women out of drinking it.
This study used a case control design which means that they recruited a group of women who had experienced stillbirth and then found another group of women who hadn’t, and looked to see whether there was anything different in their experiences. The logic is that if something is different, then that might be a protective or risk factor for stillbirth.
However, that over simplifies things. Just because something is increased in one group over another, doesn’t mean that thing causes anything. It just means there is an increase that would be interesting to look at further. It might have an effect. It might actually be linked to something else that has an effect. Or it might have no real effect at all.
This paper was accompanied by a rather scary sounding headline from the Royal College of Obstetricians and Gynecologists. ‘New research suggests caffeine raises stillbirth risk in pregnancy’, who stated that there was a ‘27% increase in stillbirth risk for each 100mg consumed, suggesting that safe limit guidelines of 200mg as recommended by NHS guidance need to be reconsidered.’
Stop right there with your scary statistics. Now this paper is interesting but it all needs to be put in context and who better than two research and birth geeks to do that for you?
A few things to bear in mind
A correlation does not mean causation. We repeat, a correlation does not mean causation. Just because two things are linked doesn’t mean one causes the other. If you’re not convinced have a look at Tyler Vigen’s Spurious correlations website for examples of daft things that correlate like the worrying correlation between margarine consumption and divorce in Maine.
- Stop with the relative risk statistics or in other words the ‘27% increase’ talk. What was the actual risk of stillbirth for an individual in the first place? A quick look tells us around 0.3% of all births. So, a 27% increase means a roughly 0.3% versus 0.4% chance. Or in other words a 99.6% chance of not having a stillbirth. That sounds far less scary.
- The study included stillbirths from all causes. Although there are potential reasons why caffeine could rarely increase the risk of growth restriction or placenta issues, we can’t see how caffeine causes maternal diabetes (although added cream & sugar might), cord prolapse, infections or a knot in the cord. These alone account for about 20% of stillbirths in the sample.
- Mothers who consumed more caffeine did have a higher risk of stillbirth. But, it’s likely that the reason for consuming lots of caffeine in pregnancy is going to have an impact on her pregnancy rather than just the caffeine. Like stress. Working night shifts. Or two jobs. Let’s change the system so pregnant women aren’t stressed rather than blaming them for decisions that they don’t have a lot of choice over.
- The biggest increase in risk was seen when mothers consumed more than 300mg of caffeine per day. For context that’s more than four instant coffees. Or eight glasses of cola. Or 11 green teas. Given the average woman’s pregnancy bladder maybe it’s simply impossible to drink that many green teas. This is above what guidelines currently recommend and indicates that these mothers may need additional support. However even when mothers regularly drank 300mg a day, the increase in risk was only 2.3 times, raising that stillbirth risk from 0.3 versus 0.7% chance of stillbirth (or again, a 99.3% chance of not having a stillbirth). This is an important issue to talk to women about but not an immediate definitive outcome for all women.
- Interestingly the researchers looked at how participants consumed caffeine. Now this is the part we are really interested in. They found an increased risk if you drank instant coffee but not if you drank filter coffee. Hmmm. Again they found an increased risk if you drank energy drinks or cola but not chai or green tea. To us this suggests that it isn’t just directly the caffeine having an impact but something about lifestyle. They collected data on maternal education but not income. Poverty is one of the biggest risk factors for stillbirth. And instant costs a lot less than filter.
So, in conclusion?
The researchers concluded that:
“Women should be informed that consumption of caffeine during pregnancy is associated with increased risk of stillbirth, particularly at levels greater than recommended by the WHO (>300 mg/day)”.
However, we conclude that:
- Women should be informed of actual individual risk and a conversation had around context and how to minimise any risk if that’s what they should like.
- Researchers should start using actual individual risk rather than percentage increases if talking to the public.
- Releasers of press releases should stop scaremongering and link to the actual conclusions i.e. an increased risk at over 300mg/day and not just ‘one cup of coffee’.
Oh, and we should look at the real risks here of poverty, stress and pressure on pregnant women and think about how we can better support them rather than scaring them into giving up their sacred morning coffee.
– Amy Brown and Sara Wickham
Conflicts of interest: Amy Brown is basically propped up by Italian filter coffee but wouldn’t touch instant with a barge pole. Sara Wickham doesn’t like coffee in any form and instead drinks rooibos tea with almond milk. Unfortunately, neither profit in any way from the sale of coffee or other drinks.
Source of funding for this post: Sadly none. Though Amy would probably cave if @LavazzaUK would like to sponsor her. Sara was once sent a box of champagne truffles by @boojabooja for mentioning that their chocolates had fuelled the writing of one of her books, but that was years ago and she has run out now.
If you’d like to learn more about unpacking research for yourself, Amy Brown has written a book called Informed is Best which helps people to read beyond the headlines and Sara Wickham teaches online courses that help midwives and birth workers to better understand birth-related research. You can find us at www.professoramybrown.co.uk and www.sarawickham.com