To the Editor.
—Dr Infante-Rivard and colleagues1 report important findings that fetal loss was not only associated with coffee intake during pregnancy, but also related to coffee intake before pregnancy. However, I am not convinced of the validity of the findings. I am concerned about potential bias and confounding.It is well known that fetal loss is strongly related to tobacco smoking and heavy consumption of alcohol, but less consistently related to caffeine consumption.2 However, the authors report that the risk of spontaneous abortion was almost identical in smokers and nonsmokers and in drinkers and nondrinkers. At the same time, they found that this risk was strongly associated with caffeine intake in this study.1-3It is important to note that the original goal of their study was not to assess the relationship between caffeine intake and fetal loss. Data on smoking, use of alcohol, and caffeine drinking
Wei M. Fetal Loss and Caffeine Intake. JAMA. 1994;272(1):27. doi:10.1001/jama.1994.03520010037015