In a case control design, the authors studied 487 women who had spontaneous abortions and 2087 controls. However, buried in the report is the fact that the blood samples that were measured were 30 years old. The blood was drawn in 1959-66 and had been stored all these years. Despite the caution such a fact suggests, caffeine is a potent drug. Even in small doses caffeine is a stimulant to the cardiovascular and nervous sytems.
Caffeine readily crosses the blood-brain barrier and the placenta.
Caffeine has a more potent effect on the fetus than on the mother because of the smaller body mass of the fetus and the inability of the fetus to metabolize caffeine. Changes in fetal heart rate and breathing patterns have been noticed even when the mother's caffeine intake is moderate and no effects are observable in the mother. A safe dose of caffeine for the fetus is unknown. Animal studies have clearly demonstrated anatomical and neurological birth defects after in utero exposure to high doses of caffeine. In 1997 the Center for Science in the Public Interest petitioned the FDA to require a listing of caffeine content on the food label.