Consumption of coffee during pregnancy

Editor—Wisborg et al's article raises more issues than it settles.¹ Firstly, coffee contains not only caffeine but a mixture of different ingredients (milk, sugar, stabilisers, flavour, and other alkaloids from coffee beans). Attributing the result of drinking coffee to just one constituent seems illogical. If Wisborg et al want to prove what they contend, they should contrast the group taking eight cups of ordinary coffee to those taking eight cups of decaffeinated coffee.

Secondly, in many parts of the world, tea, chocolate, and cola are consumed on a large scale and in high doses, like traditional Chinese tea in Hong Kong. Yet Hong Kong has one of the lowest perinatal mortality rates in the world. In Japan and China tea is regarded as part of the healthy diet, to be consumed regularly. The same also applies to cola in America and many parts of the world. So what will be the combined effect of coffee, tea, chocolate, and cola should the woman be drinking marginal amounts of coffee (four to seven cups)?

One of the gold standards in establishing causal relations between two factors is to show the dose dependent relation. Wisborg et al's study showed that, statistically speaking, there is a one off increase in stillbirth after eight or more cups of coffee. To illustrate the dose dependent relation better, the last group should have been subdivided into those taking eight to 11 cups, and those taking 12 cups or more.

Caffeine is used widely to treat migraines. If caffeine leads to stillbirth in the form of coffee, it may carry the same risk for women taking it for their migraine. Should we ban women from taking this seemingly harmless drug lest caffeine leads to stillbirth?

Lastly, I have doubts about the estimates of the number of cups of coffee per day (and hence the dose of caffeine). The size of the cup and the extent to which a cup is filled all affect the actual amount of coffee taken as does the brand. So how accurate can your estimate be?