Defined Gestational Diabetes Mellitus to Fetal Overgrowth.

We read with interest the article byBlack et al. (1) and the associatedcommentary by Ryan (2) and wish to provide some comments. Firstly, calculations by Black et al. of population attributable fractions (PAFs) of large-for-gestational-age (LGA) babies attributable to overweight/obesity and gestational di-abetesmellitus (GDM)are, as correctlynoted, largely influenced by the high prevalence of obesity (28%) and overweight (32%) in their sample. By contrast, in the Hyper-glycemia and Adverse Pregnancy Out-come study (3), conducted in 15 centers worldwide, the prevalence of obesity (14%) and overweight (22%) was much lower. Therefore, in the global context, PAFs relating to maternal BMI would be substantially lower. The inclusion by Black et al. of underweight women in the referent group and exclusion of women treated for GDM (25 % of all GDM women by the International Asso-ciation of the Diabetes and Pregnancy Study Groups criteria, including those with more marked hyperglycemia) may also have contributed to overestimation of the relative importance of obesity com-pared with GDM. Further, the PAF calculations (con-ventionally) assume that all women in the overweight and obese groups, even the most markedly obese, could revert to th