A weight gain chart for pregnant women designed in Chile.

The weight gain chart for pregnant women, developed by Rosso and Mardones (RM chart, 1997), is analysed and compared with other charts in terms of its usefulness for targeting nutritional interventions aimed at preventing low or high birth weights. The RM chart defines categories of maternal nutritional status in early gestation based on weight/height, expressed either as percentage of standard weight (PSW) or body mass index (BMI), and desirable gestational weight gains for each of these categories. Weight gain recommendations of the RM chart are proportional to maternal height. For underweight women the weight recommendation was derived from actual data, while for overweight and obese women it is based on data extrapolations. Since 1987 the Chilean National Health Service has used the RM chart as a standard in prenatal care in all its clinics, covering approximately 70% of the country's population, mostly middle and low income women. During the 1987-2001 period the proportion of underweight pregnant women and infants with birth weight < 3000 g decreased significantly and proportionally. Nevertheless, the proportion of obese pregnant women and infants with birth weight > or = 4000 g increased during this period. Multifactorial social changes including a decade of substantial economic growth in the country with improved family income, precludes the possibility of determining the efficacy of the RM chart in this group. However, the widespread use of the RM chart indicates that it is a helpful and easy-to-use instrument in the field. Further, by its clear graphical presentation of maternal nutritional status it helps draw the attention of health personnel to women who need special nutritional advice and support.