The American public consumes a wide array of caffeinated products as coffee, tea, chocolate, cola beverages, and caffeine-containing medication. Therefore, it seems of value to inform both the scientific community and the consumer about the potential effects of excessive caffeine consumption, particularly by pregnant women. The results of this literature review suggest that heavy caffeine use (> or = 300 mg per day) during pregnancy is associated with small reductions in infant birth weight that may be especially detrimental to premature or low-birth-weight infants. Some researchers also document an increased risk of spontaneous abortion associated with caffeine consumption prior to and during pregnancy. However, overwhelming evidence indicates that caffeine is not a human teratogen, and that caffeine appears to have no effect on preterm labor and delivery. More research is needed before unambiguous statements about the effects of caffeine on pregnancy outcome variables can be made.