Government advice to pregnant women to cut back on caffeine may be too cautious, according to new research.

Pregnant women are advised to drink no more than three mugs of instant coffee a day and are often urged to cut out caffeine altogether because of fears that it can cause premature birth and low birth weight.

But Danish researchers have concluded that higher intake of caffeine has no impact on birth weight or gestational period.

A total of 1,207 women who were fewer than 20 weeks pregnant and drank more than three cups a day were recruited by researchers from the University of Aarhus. Half drank decaffeinated and the other half coffee with caffeine.

The women were monitored to ensure they were not consuming other products containing caffeine. The study found no significant difference in the proportion who had either premature babies or babies with low birth weights.

The study, published online by the British Medical Journal, says: "No significant differences were found for mean birth weight or mean length of gestation between [the two groups]."

Caffeine remains in women's blood longer if they are pregnant and is passed through the placenta to the foetus. Government advice is to reduce caffeine consumption, but the Food Standards Agency says three mugs a day is fine - as long as no other caffeine is consumed.