A large study recently published in the American Journal of Obstetrics and Gynecology has found that too much caffeine during pregnancy can double the risk of miscarriage. Women at risk of too much caffeine were consuming two cups of brewed coffee or four cups of black tea a day or more. 12.5% of women who consumed no caffeine miscarried wheras 24.5% of women who consumed 200mg of caffeine or more a day miscarried.

The study does not make recommendations but no caffeine in pregnancy would seem to be advisable.