Implications for practice and research

• The findings indicate that caffeine intake should be avoided during pregnancy.

• Research is needed to clarify how advice on caffeine abstinence should be framed to be most effective and to evaluate the actual effectiveness of such advice.

Context

Caffeine is a widely consumed psychoactive substance. Although controversy exists concerning some implications of caffeine consumption during pregnancy, questions concerning maternal caffeine and low birth weight have been largely settled. This study adds further weight to an otherwise consistent conclusion. Using meta-analysis involving 13 prospective studies consisting of more than 100 000 participants from Europe, Canada or the USA, Chen and colleagues assessed the dose–response relationship between maternal caffeine consumption and risk of low birth weight (<2500 g). The analyses indicated that for each 100 mg/day increment in maternal caffeine intake (about one cup of coffee) there was a 13% higher risk of low birth weight.

Findings

The analysed studies were judged to have included comprehensive controls against potential confounders, including: gestational age, fetal gender, maternal characteristics of age, weight, height, parity, smoking, alcohol intake and socioeconomic status. Results indicated a linear relationship, where higher maternal caffeine intake during pregnancy was associated with a higher risk of delivering low birth weight infants. Compared with the reference category of no or very low caffeine consumption, birth weight was 9, 33 and 69 g lower in the low, moderate and high caffeine consumption groups, respectively.

Commentary

The diverse pharmacological effects of caffeine, the fact that it readily crosses the placenta and the relative inability of the fetus to metabolise it, all point to the possibility of its adverse effects during pregnancy. In 1980, the Food and Drug Administration in the USA issued a warning to women about consuming caffeine during pregnancy. That advice was largely predicated on the precautionary principle, given that the evidence available at that time was mostly suggestive.

In 1985, an early systematic review concluded that there was tentative support that caffeine contributes to fetal growth restriction and low birth weight.1 It highlighted various methodological shortcomings in the then existing literature and called for more research employing improved methods for measuring caffeine exposure and better controls against potential confounders, especially alcohol and tobacco use. An updated review published 6 years later concluded that the evidence had strengthened and another review published 6 years after that concluded that the evidence had become ‘strong’.2 ,3 Since then, new studies have been conducted, and this latest meta-analysis by Chen and colleagues provides further confirmation of the now scientifically robust finding that maternal caffeine contributes to low birth weight.

Although the potential for caffeine to contribute to low birth weight has high biological plausibility, there is always the possibility of residual confounding in observational studies. However, the robustness of the association in this instance militates against confounding.

Moreover, the existence of a dose–response relation is suggestive of causation and there is no indication of a threshold effect. Therefore, recommendations advising ‘moderation’ (ie, to reduce consumption to ‘low’ or ‘moderate’ levels) are without scientific foundation. Taking account of all the relevant science, the only justifiable recommendation that can be made is for caffeine abstinence during pregnancy.

In this context, caffeine abstinence refers specifically to avoidance of coffee, tea, cola and other caffeine-containing sodas, and caffeine-containing ‘energy’ drinks. The low caffeine content of chocolate and chocolate confectionaries, chocolate cake, hot chocolate, and decaffeinated coffee and tea is such that these products generally need not form part of the maternal caffeine-avoidance regimen.2 ,3