title: Gestational bodyweight gain among underweight Japanese women related to small-for-gestational-age birth.
abstract: OBJECTIVE
  The prevalence of underweight women, who have an increased risk for small-for-gestational-age (SGA) birth, is increasing in Japan. We examined the associations of pre-pregnancy body mass index and gestational weight gain (GWG) with SGA birth among Japanese women.
  
  
  METHODS
  We conducted a prospective cohort study of 1391 women who delivered full-term singleton babies. SGA was defined as below the 10th percentile of birthweight at each gestational age, baby sex, and parity. We calculated the 5th percentile of birthweight in the same way for another threshold for SGA. According to pre-pregnancy body mass index, we divided the participants into three groups: underweight (<18.5 kg/m(2)), normal weight (18.5-24.9 kg/m(2)), and overweight and obese (≥25.0 kg/m(2)).
  
  
  RESULTS
  SGA birth was observed most frequently among the underweight group (13.8%). Underweight was associated with an increased risk of SGA birth. The multiple-adjusted odds ratio for underweight was 1.96 (95% confidence interval, 1.23-3.11) compared with normal weight. Sufficient GWG reduced the incidence and the multiple-adjusted odds ratio for 1-kg increase of GWG was 0.86 (0.81-0.92). The same tendency was observed for the delivery of infants below the 5th birthweight percentile. Women with underweight and normal weight who had 9.0 kg or less of GWG had a significantly higher risk of SGA birth than women with normal weight who had 9.1-11.0 kg of GWG.
  
  
  CONCLUSIONS
  Underweight and poor GWG were associated with a higher incidence of SGA birth. However, the incidence of SGA birth among underweight women was not increased significantly if they had sufficient GWG.
authors.affiliation: Department of Preventive Medicine and Environmental Health, Osaka City University Graduate School of Medicine, Osaka, Japan. haritan@med.osaka-cu.ac.jp
authors.forename: Nobuko
authors.initials: N
authors.lastname: Harita
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Kariya
authors.forename: Tomoshige
authors.initials: T
authors.lastname: Hayashi
authors.forename: Kyoko Kogawa
authors.initials: KK
authors.lastname: Sato
authors.forename: Takuya
authors.initials: T
authors.lastname: Aoki
authors.forename: Kimihiko
authors.initials: K
authors.lastname: Nakamura
authors.forename: Ginji
authors.initials: G
authors.lastname: Endo
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Narimoto
mesh_terms: D000293:Adolescent; D000328:Adult; D015992:Body Mass Index; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D007236:Infant, Small for Gestational Age; D007564:Japan; D015999:Multivariate Analysis; D011247:Pregnancy / Q000502:physiology*; D011446:Prospective Studies; D013851:Thinness / Q000503:physiopathology*; D015430:Weight Gain; D055815:Young Adult