title: Maternal smoking during pregnancy and childhood growth trajectory: a random effects regression analysis.
abstract: BACKGROUND
  Although maternal smoking during pregnancy has been reported to have an effect on childhood overweight/obesity, the impact of maternal smoking on the trajectory of the body mass of their offspring is not very clear. Previously, we investigated this effect by using a fixed-effect model. However, this analysis was limited because it rounded and categorized the age of the children. Therefore, we used a random-effects hierarchical linear regression model in the present study.
  
  
  METHODS
  The study population comprised children born between 1 April 1991 and 31 March 1999 in Koshu City, Japan and their mothers. Maternal smoking during early pregnancy was the exposure studied. The body mass index (BMI) z-score trajectory of children born to smoking and non-smoking mothers, by gender, was used as the outcome. We modeled BMI trajectory using a 2-level random intercept and slope regression.
  
  
  RESULTS
  The participating mothers delivered 1619 babies during the study period. For male children, there was very strong evidence that the effect of age in months on the increase in BMI z-score was enhanced by maternal smoking during pregnancy (P < 0.0001). In contrast, for female children, there was only weak evidence for an interaction between age in months and maternal smoking during pregnancy (P = 0.054), which suggests that the effect of maternal smoking during pregnancy on the early-life BMI trajectory of offspring differed by gender.
  
  
  CONCLUSIONS
  These results may be valuable for exploring the mechanism of fetal programming and might therefore be clinically important.
authors.affiliation: Center for Birth Cohort Studies, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Yamanashi, Japan. kohtas@yamanashi.ac.jp
authors.forename: Kohta
authors.initials: K
authors.lastname: Suzuki
authors.forename: Naoki
authors.initials: N
authors.lastname: Kondo
authors.forename: Miri
authors.initials: M
authors.lastname: Sato
authors.forename: Taichiro
authors.initials: T
authors.lastname: Tanaka
authors.forename: Daisuke
authors.initials: D
authors.lastname: Ando
authors.forename: Zentaro
authors.initials: Z
authors.lastname: Yamagata
mesh_terms: D015992:Body Mass Index; D002648:Child; D002657:Child Development; D002675:Child, Preschool; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007231:Infant, Newborn; D007564:Japan / Q000453:epidemiology; D008297:Male; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects / Q000453:epidemiology; D012044:Regression Analysis; D012727:Sex Characteristics; D012907:Smoking / Q000009:adverse effects* / Q000453:epidemiology; D015430:Weight Gain