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Re: "Associations of gestational weight gain with short- and longer-term maternal and child health outcomes".

We read with interest the relevant article by Oken et al. (1), where they examined the association of gestational weight gain with shortand longer-term maternal and child health outcomes. Their positive findings are of great importance, but we wonder whether this result might, at least partially, be influenced by lifestyle factors that are known to influence gestational weight gain, namely, physical activity. Their compelling database—from the Project Viva—gives the possibility to assess this potential confounder. In fact, they recently published another study with the same cohort where they showed that midpregnancy walking and vigorous physical activity (assessed by self-reported questionnaires) were inversely associated with excessive gestational weight gain (2). Using a randomized controlled trial design, we recently observed that overweight (body mass index 1⁄4 25– 29.9 kg/m) sedentary gravidae (controls) gained more weight (~1.4 kg) than their physically active referents (3), in agreement with the results of Stuebe et al. (2). Further, sedentary women gained ~0.8 kg more than the Institute of Medicine recommendations for gestational weight gain (4). We also showed that maternal prepregnancy body weight was positively and significantly associated with newborns’ birth weight in the sedentary group (b 1⁄4 19.201; P 1⁄4 0.01) but not in the active group (b 1⁄4 4.559; P 1⁄4 0.281) (3). In contrast, in other reports with the same cohort, we found that physical activity does not affect gestational age (5), maternal anemia (6), or type of delivery (7). It would be interesting, therefore, if Oken et al. (1) could consider whether physical activity is a potential confounder of the relation they observed between gestational weight gain and maternal and child health outcomes. To understand to what extent the lifestyle adopted by the mother over the pregnancy affects the offspring’s health later in life is of clinical and public health interest. As such, the contribution by Oken et al. (1) is to be acknowledged.