Abstract
The inherent correlation between the total amount of weight gained in pregnancy and the duration of pregnancy creates major methodological challenges in the study of pregnancy weight gain. In this issue (Am J Epidemiol. 2022;191(10):1687-1699), Richards et al. examine the extent to which different measures of pregnancy weight gain (including covariate adjustment for gestational age and standardizing weight gain for gestational duration using a pregnancy weight gain chart) are able to disentangle the effects of low weight gain on perinatal health from the role of younger gestational age at delivery for 3 outcomes: small-for-gestational-age birth, cesarean delivery, and low birth weight. While methodological research to understand how to best disentangle the effects of gestational weight gain from pregnancy duration is valuable, we argue that the practical utility of this type of research would be increased by aligning the specific research questions more closely with health outcomes on which evidence is most needed-those not considered in current weight gain guidelines due to lack of high-quality evidence (such as pre-eclampsia and stillbirth). Further, evaluations of weight gain charts should separate out the potential for bias introduced by the use of a normative chart per se from the use of a chart unsuitable for the study population.