Gestational weight gain charts: results from the Brazilian Maternal and Child Nutrition Consortium

Abstract

Background: Monitoring gestational weight gain (GWG) is fundamental to ensure a successful pregnancy for the mother and the offspring. There are several international GWG charts, but just a few for low- and middle-income countries.

Objectives: To construct GWG charts according to pre-pregnancy BMI for Brazilian women.

Methods: This is an individual patient data analysis using the Brazilian Maternal and Child Nutrition Consortium data, comprising 21 cohort studies. External validation was performed using "Birth in Brazil," a nationwide study. We selected adult women with singleton pregnancies who were free of infectious and chronic diseases, gestational diabetes, and hypertensive disorders; who delivered a live birth at term; and whose children were adequate for gestational age, and with a birth weight between 2500-4000 g. Maternal self-reported pre-pregnancy weight and weight measured between 10-40 weeks of gestation were used to calculate GWG. Generalized Additive Models for Location, Scale and Shape were fitted to create GWG charts according to gestational age, stratified by pre-pregnancy BMI.

Results: The cohort included 7086 women with 29,323 weight gain measurements to construct the charts and 4711 women with 31,052 measurements in the external validation. The predicted medians for GWG at 40 weeks, according to pre-pregnancy BMI, were: underweight, 14.1 kg (IQR, 10.8-17.5 kg); normal weight, 13.8 kg (IQR, 10.7-17.2 kg); overweight, 12.1 kg (IQR, 8.5-15.7 kg); obesity, 8.9 kg (IQR, 4.8-13.2 kg). The 10th, 25th, 50th, 75th, and 90th percentiles were estimated. Results for internal and external validation showed that the percentages below the selected percentiles were close to those expected.

Conclusions: The charts proposed provide a description of GWG patterns according to gestational age and pre-pregnancy BMI among healthy Brazilian women with good neonatal outcomes. The external validation indicates that this new tool can be used to monitor GWG in the primary health-care setting and to test potential recommended values.

Keywords: gestation; gestational weight gain; pregnancy; primary health care; reference standards; weight gain.

FIGURE 1

Equation to extract z-scores from GAMLSS models (Box-Cox t and Box-Cox Power Exponential distributions). The constant added to all models was 20 kg. Abbreviations: GAMLSS, Generalized Additive Models for Location, Scale, and Shape; GWG, gestational weight gain; L, lambda (or nu), M, mu; S, sigma.

FIGURE 2

Sample size for the construction of the charts. “Measurements” refer to information of both gestational age and weight gain. Underweight, BMI < 18.5; normal weight, BMI ≥ 18.5 and < 25.0; overweight, BMI ≥ 25.0 and < 30.0; and obesity, BMI ≥ 30.0. Abbreviations: LBW, low birth weight; LGA, large for gestational age; SGA, small for gestational age.

FIGURE 3

Sample size according to gestational age for each maternal pre-pregnancy BMI group (underweight, BMI < 18.5; normal weight, BMI ≥ 18.5 and < 25.0; overweight, BMI ≥ 25.0 and < 30.0; and obesity, BMI ≥ 30.0).

FIGURE 4

Gestational weight gain charts according to pre-pregnancy BMI for Brazilian women, using data from the Brazilian Maternal and Child Nutrition Consortium. The gray dots represent each weight gain measurement used in the construction of the charts. (A) Underweight (BMI < 18.5; n = 1849 measurements); (B) normal weight (BMI ≥ 18.5 and < 25.0; n = 18,252 measurements); (C) overweight (BMI ≥ 25.0 and < 30.0; n = 6754 measurements); and (D) obesity (BMI ≥ 30.0; n = 2468 measurements).