Gestational weight gain monitoring curves: Predictive capacity to capture adverse infant outcomes and longitudinal analysis in a large Brazilian prospective study

Introduction: The diagnosis and nutritional follow-up of pregnant women are procedures which should be part of prenatal routine, qualifying the health assistance offered. Internationally, there is a vast debate regarding the choice of new indicators of weight gain. In Brazil and in several Latin American countries, the Atalah’s curve has been recommended. However, it presents limitations which justify its replacement. Objective: To evaluate the capacity of Atalah's curve in capturing adverse infant outcomes, and to offer elements for the debate regarding the creation of an international curve for monitoring gestational weight gain. Methods: Analyses were based in data of 4,540 pregnant women, collected by the Brazilian Study of Gestational Diabetes, a prospective cohort investigation which took place in six Brazilian state capitals between 1991-1995, and comprised over 23,000 repeated measurements of body mass index (BMI). Small-for-gestational-age, low birth weight, large-for-gestational-age and macrosomia were selected as outcomes. Analyses employed two methodologies: Receiver Operating Characteristic (ROC) Curve and mixed-effect models for repeated measures. Findings: ROC curves revealed that the gross area under the curve was always < 0.70, the minimum value of acceptable sensitivity and specificity for the determination of cut-off points with good predicting capacity. The sensitivity and specificity to predict any of the four outcomes was low. Models with mixed effects showed a mean BMI rate gain of 0.155 kg/m² per week throughout gestation, a gain of 4.4 units attributable to pre-pregnancy BMI, and gains for the women surveyed in the study always smaller than those of Atalah's curve, independently of the pre-pregnancy nutritional status. Conclusion: The curve presents a low capacity of predicting adverse infant outcomes, what suggests the importance of creating an international curve which would be able to serve as a reference in the assessment and nutritional follow-up of pregnant women.