03 Aug 2010

Caffeine intake during pregnancy

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Caffeine is pretty much my favourite substance in the whole world. I try to start every day with a long black and after two double shot coffees I tend to move on to tea for the rest of the day.

The issue of caffeine use in pregnancy has been around for a while and many authorities advise women to reduce their caffeine intake or eliminate its use altogether. The scientific literature is a little conflicting on this topic however so I am a little more circumspect.

One cup of coffee is said to contain about 100 mg of caffeine (although I suspect the double shot long blacks from Clodeli contain somewhat more). One cup of tea contains about 50 mg and caffeine is also found in cola, some “energy drinks”, chocolate and cocoa.

On one hand large doses of caffeine cross the placenta and may cause reduced fetal growth, miscarriages and stillbirths. The studies that made this finding need to be interpreted carefully because they did not adequately control for other harmful habits such as smoking, stress and long work hours. Indeed one study from 2007 showed that reducing caffeine intake from at least three cups of coffee per day to almost nil (by switching to decaf) did not reduce the likelihood of giving birth either prematurely or to an abnormally small baby.

Then again a more recent study in the British Medical Journal (www.bmj.com) showed that women taking more than 300 mg caffeine had a higher rate (about 50% more likely) of giving birth to a baby that was small for its gestational age when compared to women taking less than 100 mg.

By the way you may be asking what the big issue is about giving birth to a small for dates baby. Well being small usually (but not always) reflects poor placental function so smaller babies are at increased risk of stillbirths, fetal distress in labour and some problems in early or even adult life (including diabetes and high blood pressure).

So, where does all of this leave us?

Well we now know that caffeine crosses the placenta and it is potentially harmful to the baby – although it is difficult to quantify the risk of harm and not all studies have demonstrated harm. A pragmatic approach to this issue would be to reduce your caffeine intake during pregnancy to one cup of coffee or two cups of tea per day. Remember that hot chocolates and Diet Cokes etc also contain coffee and that replacing your caffeine intake with sugary drinks is not a particularly healthy approach.


Olsen J and Bech BH. Editorial: Caffeine intake during pregnancy. British Medical Journal 3 November 2008; 337:a2316

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