LETTER TO THE EDITOR

ART and major structural birth defects in the United States Sir, We read with interest the study by Reefhuis et al. (2009) showing that assisted reproductive technology (ART) treatment is a risk for struc-tural birth defects. The authors recognize that this risk may be over-stated because underlying subfertility may in itself be an important risk factor for such defects. In our meta-analysis of 19 studies (Rimm et al., 2004), where we found an overall risk of 1.29, we noted the failure of each of those 19 studies to use the most appro-priate control group, namely infertile couples conceiving spontaneously. Responding to the concern we raised, Zhu et al. (2006) attempted to design an analysis with a control group made up of subfertile couples. They compared three groups of children: those born o