Dynamic energy-balance model predicting gestational weight gain

Abstract

Background: Gestational weight gains (GWGs) that exceed the 2009 Institute of Medicine recommended ranges increase risk of long-term postpartum weight retention; conversely, GWGs within the recommended ranges are more likely to result in positive maternal and fetal outcomes. Despite this evidence, recent epidemiologic studies have shown that the majority of pregnant women gain outside the target GWG ranges. A mathematical model that predicts GWG and energy intake could provide a clinical tool for setting precise goals during early pregnancy and continuous objective feedback throughout pregnancy.

Objective: The purpose of this study was to develop and validate a differential equation model for energy balance during pregnancy that predicts GWG that results from changes in energy intakes.

Design: A set of prepregnancy BMI-dependent mathematical models that predict GWG were developed by using data from a longitudinal study that measured gestational-changes in fat-free mass, fat mass, total body water, and total energy expenditure in 63 subjects.

Results: Mathematical models developed for women with low, normal, and high prepregnancy BMI were shown to fit the original data. In 2 independent studies used for validation, model predictions of fat-free mass, fat mass, and total body water matched actual measurements within 1 kg.

Conclusions: Our energy-balance model provides plausible predictions of GWG that results from changes in energy intakes. Because the model was implemented as a Web-based applet, it can be widely used by pregnant women and their health care providers.

FIGURE 1.

Group mean gestational weights (±SDs) from the study of Butte et al (24, 25) were plotted and compared with the gestational duration for each BMI category. Error bars represent SDs. Gestational weights of women classified by pregravid BMI are depicted as follows: low BMI (in kg/m²) (≤19.8) (A), normal BMI (19.8 < BMI < 26) (B), and high BMI (≥26) (C).

FIGURE 2.

Mean values for FFM, FM, and TBW throughout pregnancy predicted from mean pregravid age, weight, and height for women in the studies of Goldberg et al (22) and Kopp-Hoolihan et al (23). Error bars represent SDs. A: Model comparisons with the study of Goldberg et al (22). B: Model comparisons with the study of Kopp-Hoolihan et al (23). The study of Goldberg et al (22) did not report longitudinal TBW. FFM, fat-free mass; FM, fat mass; TBW, total body water.

FIGURE 3.

Model-predicted GWG compared with gestational duration on the basis of simulations of different energy-intake recommendations for a normal-weight woman [age: 32 y; height: 163 cm; BMI (in kg/m²): 23]. Dashed lines represent lower and upper ranges of the 2009 IOM-recommended GWG (in kg) (3). A: Model prediction of GWG that applied an additional intake of 300 kcal/d (28, 32). B: Model simulations that applied an IOM dietary reference additional energy intake (340 kcal/d in the second trimester and 460 kcal/d in the third trimester); the WHO recommendation (33) of an additional 117-kcal/d energy intake was assumed in the first trimester. C: Model simulations for the FAO/WHO/United Nations University (33) recommended additional energy intake of 117, 360, and 475 kcal/d in the first, second, and third trimesters, respectively. GWG, gestational weight gain; IOM, Institute of Medicine.

FIGURE 4.

Screen shot of Web-based applet developed to simulate model predictions. The user enters prepregnancy age, height, weight, and trimester energy intake (kcal/d). Model predicted weight by pregnancy week is the blue curve. The IOM weight range is depicted as the green zone within the graph. Panel A is a simulation for a subject age 32, height 163 cm, and prepregnancy weight 70 kg. Additional energy intake is set at 398 kcal/d, 383 kcal/d, and 391 kcal/d in the first, second, and third trimesters, respectively. Maternal weight exceeds the IOM guidelines as indicated by the blue curve located above the green zone. In Panel B, additional energy intake is lowered to 148, 291, and 341 kcal/d during the first, second, and third trimesters, respectively. Maternal weight under the adjusted energy intake is within the IOM guidelines as the blue curve now lies within the green zone. The applet can be accessed at: https://www.pbrc.edu/the-research/tools/gwg-predictor/. cal, calorie; cal., calorie; Init. initial; IOM, Institute of Medicine; tri., trimester; Wt, weight.