The maternal weight gain chart proposed by Rosso and Mardones (RM) was subsequently modified by Atalah et al. (AEA). Both charts are widely used in Latin America. The purpose of this study was to compare birth length (BL) and birth weight (BW) outcomes of both charts. A prospective study of pregnant women and their offspring’s was performed in Santiago, Chile. From a total sample of 27,613 pregnant women a sub-sample of 11,465 term healthy singleton pregnant women was selected for additional analyses. κ statistics was used to study the degree of agreement of both charts in the diagnosis of maternal nutritional status. Obese and underweight women were classified using both standards at the beginning of pregnancy and compared in terms of BL<50 cm, BW<3000 g and BW>4250 g proportions. Sensitivity and specificity values of at risk newborns, whose categories were considered as gold standard, were obtained for obese and underweight women of each chart. There was a moderate agreement in the nutritional classification of these charts. Proportions of BL<50 cm and both BW<3000 g and>4250 g were similar at each nutritional category; however, absolute figures for at risk newborns were much higher in the RM underweight and obese women. The RM chart showed higher sensitivity values than the AEA chart. The higher sensitivity of the RM chart would support its use for prevention purposes. This chart is advisable for Latin American countries and also for most developing countries.