Physical and socioeconomic predictors of birthweight in Japan

Background: The purpose of this study was to characterize physical and socioeconomic factors associated with birthweight in Tokyo, Japan. Methods: In a cohort of obstetric outpatients from the Tokyo Metropolitan Maternity and Child Health Institute, Tokyo, and The Jikei University School of Medicine, Chiba, Japan, 553 eligible women in their third trimester of pregnancy were given a survey investigating physical and socioeconomic backgrounds. Results: Infants tended to be small for gestational age when maternal pre-pregnancy weight was lower, and low income and female infant gender were significantly associated with a low birthweight infant. Further, birthweight compared with predicted birthweight was lower in the case of a female infant gender, low income, low maternal pre-pregnancy weight and low parity. Conclusion: Income is a novel parameter that is associated with birthweight in Japan.