Caffeine Use During Pregnancy: How Much Is Safe?

To the Editor. —The article by Mills et al¹ is one of the first prospective evaluations of the relationship of caffeine use and reproductive outcomes and, thus, is an important contribution to the field. However, we have concerns about the authors' conclusions.

First, the results of this study are inconsistent with many of the findings previously reported. Nine of 12 studies representing a variety of populations and study designs found a relationship between maternal caffeine consumption and low birth weight or intrauterine growth retardation (IUGR), although the evidence for the relationship of caffeine and spontaneous abortion (SAB) is less consistent.² Both decreased birth weight and an increase in SAB have been reported in monkeys consuming caffeine in drinking water at concentrations within the range of human exposure.³ There are a number of biologically plausible mechanisms for caffeine to adversely affect both of these end points, eg, vasoconstriction