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

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.