One cup of fresh coffee a day significantly increases the chances of giving birth to an underweight baby.
The new findings from a Scandinavian study suggest current guidelines on caffeine consumption during pregnancy may not go far enough.
A daily dose of between 200 and 300 milligrammes of caffeine – equivalent to one cup of coffee – increased the risk of a baby being small for gestational age by up to 62pc. At present, the World Health Organisation recommends a consumption limit of 300mg per day.
Writing in the online journal 'BMC Medicine', the researchers said: "This association should be further investigated and recommendations might have to be re-evaluated."