Sato N, et al. - Given that in Japan, an appropriate increase in gestational weight gain (GWG) for underweight women may prevent low birth weight and that the current strategy aims at raising the desired value of GWG equally for all pregnant women within the underweight category, researchers here examined whether or not the relationship between GWG and birth weight for gestational age (BW/GA) are uniformly equivalent for all the women. In this retrospective cohort analysis, women who delivered their newborns at Tokyo Medical and Dental University Hospital from 2013 to 2017, were assessed. The analysis revealed no correlation of the inter-pregnancy difference in BW/GA with that of GWG. However, there was a high correlation between BW/GA of siblings. Women who delivered larger-sized newborns exhibited a higher correlation between GWG and BW/GA than women who delivered smaller-sized newborns. Findings thereby suggest a positive correlation of GWG with BW/GA for heavier neonates whose birth weights were similar to the average neonatal weight according to world standards. However, caution should be practiced for low-birth-weight neonates because increased GWG does not always result in improved birth weight.