Too much caffeine during pregnancy may double the risk of miscarriage. In an American cohort study, 1,063 pregnant women were interviewed about their caffeine intake. An increasing dose of daily caffeine during pregnancy was associated with an increased risk of miscarriage, compared with no caffeine intake. Of 264 women who had consumed no caffeine, 12.5% had miscarriages. The miscarriage rate was 24.5% in the 164 women who consumed 200 mg (equivalent to less than two cups of brewed coffee or four cups of black tea) or more per day. (Maternal caffeine consumption during pregnancy and the risk of miscarriage: a prospective cohort study. Am J Obstet Gynecol. 2008 Mar;198(3):279.e1-8).