Kato N, Sauvaget C, Yoshida H, et al. - Since birthweight has been consistently declining in Japan for more than 30 years, researchers sought to investigate the period during which birthweight rapidly decreased and to identify factors contributing to the marked decline. They retrieved 40,968,266 birth certificates of neonates born between 1980 and 2004 using population-based birth certificate data from vital statistics records. From 1980 to 2004, the mean birthweight declined in Japan, particularly between 1990 and 1999. Trends in gestational age, gender, birth order, multiple gestations, and fathers' age did not completely explain recent decreases in birthweight among Japanese neonates. As a result, additional factors such as pre-pregnancy maternal BMI and maternal diet should be considered. Reducing the rate of induced deliveries and improving young women's BMI or diet should be a public health priority.