Gestational Weight Gain-for-Gestational Age Z-Score Charts Applied across U.S. Populations

Abstract

Background: Gestational weight gain may be a modifiable contributor to infant health outcomes, but the effect of gestational duration on gestational weight gain has limited the identification of optimal weight gain ranges. Recently developed z-score and percentile charts can be used to classify gestational weight gain independent of gestational duration. However, racial/ethnic variation in gestational weight gain and the possibility that optimal weight gain differs among racial/ethnic groups could affect generalizability of the z-score charts. The objectives of this study were (1) to apply the weight gain z-score charts in two different U.S. populations as an assessment of generalisability and (2) to determine whether race/ethnicity modifies the weight gain range associated with minimal risk of preterm birth.

Methods: The study sample included over 4 million live, singleton births in California (2007-2012) and Pennsylvania (2003-2013). We implemented a noninferiority margin approach in stratified subgroups to determine weight gain ranges for which the adjusted predicted marginal risk of preterm birth (gestation <37 weeks) was within 1 or 2 percentage points of the lowest observed risk.

Results: There were minimal differences in the optimal ranges of gestational weight gain between California and Pennsylvania births, and among several racial/ethnic groups in California. The optimal ranges decreased as severity of prepregnancy obesity increased in all groups.

Conclusions: The findings support the use of weight gain z-score charts for studying gestational age-dependent outcomes in diverse U.S. populations and do not support weight gain recommendations tailored to race/ethnicity.

Keywords: ethnic groups; gestational age; growth charts; pregnancy; premature birth; weight gain.

Figure 1.

Adjusted predicted marginal risks of preterm birth per 100 live births in (a) California and (b) Pennsylvania women who were normal weight (BMI 18.5–24.9 kg/m²) before pregnancy. Solid curved lines represent point estimates and dashed curved lines represent 95% confidence intervals. The inside vertical lines represent the noninferiority margins for a 1% risk difference and the outside vertical lines represent the noninferiority margins for a 2% risk difference.

Figure 2.

Optimal gestational weight gain ranges at term (40 weeks’ gestation) for lowest preterm birth risk corresponding to noninferiority margins of 1% risk difference. Solid lines represent California and dashed lines represent Pennsylvania. Data for low and high weight gains in Pennsylvania underweight and obese class 3 were sparse.

Figure 3.

Optimal gestational weight gain ranges at term (40 weeks’ gestation) for lowest preterm birth risk corresponding to noninferiority margins of 1% risk difference in California births to women who were normal weight (BMI 18.5–24.9 kg/m²) before pregnancy.