LONDON -- November 4, 2008 -- Consuming caffeine at any time during pregnancy is associated with an increased risk of fetal growth restriction (FGR), according to a study published on bmj.com.
Although previous studies have also shown this to be true, the current study shows that any amount and any type of caffeine intake -- from tea, cola, chocolate, cocoa, and some prescription drugs -- is linked with relatively slower fetal growth.
Justin Konje, MD, and colleagues from the University of Leicester, Leicester, United Kingdom, as well as collaborators from the University of Leeds, Leeds, United Kingdom, examined the association of maternal caffeine intake and individual caffeine metabolism on fetal birth weight.
The authors recruited 2,645 low-risk pregnant women (mean age, 30 years) who were between 8 and 12 weeks pregnant from 2 large UK teaching hospitals between September 2003 and June 2006.
They used a caffeine-assessment tool (CAT) to record caffeine intake from all possible dietary sources in the 4 weeks before and throughout pregnancy and conducted a saliva sample test to calculate individual caffeine metabolism.
Results showed that the average caffeine intake during pregnancy was 159 mg/day. Interestingly, 62% of the caffeine use reported came from tea. Other sources were coffee (14%), cola (12%), chocolate (8%), and soft drinks (2%).
Most of the babies were born at full term, with an average birth weight of 3,450 g, while 4% were born prematurely, 0.3% were stillborn, and 0.7% were miscarried late. Overall, the results confirmed that these were low-risk pregnancies. However, the authors found a "dose-response relationship" showing that increased caffeine intake was associated with increased risk of FGR.
Compared with pregnant women consuming <100 mg/day of caffeine, the risk estimates of having a lower birth weight baby increased by 20% for intakes of 100 to 199 mg/day; by 50% for those taking between 200 to 299 mg/day, and by 40% for >300 mg/day.
There was no level of caffeine intake at which the increased risk of FGR stopped increasing during pregnancy. Caffeine consumption of >100 mg/day -- the equivalent of 1 cup of coffee -- was associated with a reduction in birth weight of 34 to 59 g in the first trimester, 24 to 74 g in the second, and about 66 to 89 g in the third trimester. This effect was significant and consistent across all trimesters with caffeine consumption of >200 mg/day. The authors also note that the link between caffeine and FGR was stronger in women who metabolised caffeine more quickly.
The authors explain that, although these reductions in birth weight may seem small given that the average birth weight is over 3 kg, a drop of 60 to 70 g might be important for a baby who was already small and at risk.
Pregnant women should make every effort to reduce their caffeine consumption significantly before and during pregnancy, the authors warn.
In light of this evidence, the UK Food Standards Agency is altering its guidance on the recommended daily limit of caffeine consumption and reducing it from 300 to 200 mg.
SOURCE: BMJ
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