A study published in the American Journal of Obstetrics and Gynaecology found 200mg of caffeine a day doubled the risk of miscarriage.
The British Food Standards Agency guidelines recommend no more than four cups of coffee a day during pregnancy.
The study — conducted by Dr De-Kun Li — involved 1,063 women who had become pregnant in the past month or two.
The women kept a diary about their caffeine intake up to their 20th week of pregnancy.
By 20 weeks, 172 of the women had miscarried.
Compared with those who did not drink caffeine, women who consumed up to 200mg a day had an increased risk of miscarriage.
For women who drank more than 200mg the risk increased from 15% to 25%.
Dr Li said: “The main message for pregnant women is they probably should consider stopping caffeine consumption during pregnancy.”
Pat O’Brien, a consultant obstetrician at University College Hospital, London, and spokesman for the Royal College of Obstetricians and Gynaecologists, said: “I will advise patients to avoid caffeine completely, at least for the first 12 weeks of pregnancy.”