title: Body composition, smoking, and spontaneous dizygotic twinning.
abstract: OBJECTIVE
  To examine differences in body composition and smoking between mothers of spontaneous monozygotic and dizygotic twins, while taking into account maternal age, gravidity, and educational attainment.
  
  
  METHODS
  Retrospective cohort study.
  
  
  METHODS
  The Netherlands Twin Register.
  
  
  METHODS
  Mothers of twins (n = 19,357) registered with the Netherlands Twin Register. Data were selected from mothers of spontaneous monozygotic twins (MZ; n = 5663) and mothers of spontaneous dizygotic twins (DZ; n = 8515).
  
  
  METHODS
  None.
  
  
  METHODS
  The odds of having spontaneous DZ twins versus spontaneous MZ twins as a function of height, body mass index (BMI), and smoking before pregnancy, after accounting for age, gravidity, and educational attainment.
  
  
  RESULTS
  Compared with spontaneous MZ twinning, spontaneous DZ twinning is significantly associated with increasing height (odds ratio, 1.6; 95% confidence interval [CI], 1.5-1.8 for the tallest versus the shortest height quartile), an increased BMI (odds ratio, 1.3; 95% CI, 1.1-1.4 for overweight vs. normal weight), and smoking before the twin pregnancy (odds ratio, 1.4; 95% CI, 1.3-1.5 for smoker vs. nonsmoker). Maternal age and gravidity, but not educational attainment, had to be included in the model.
  
  
  CONCLUSIONS
  Spontaneous dizygotic twinning is associated with body composition and smoking.
authors.affiliation: Department of Biological Psychology, VU University Amsterdam, Amsterdam, The Netherlands.
authors.forename: Chantal
authors.initials: C
authors.lastname: Hoekstra
authors.forename: Gonneke
authors.initials: G
authors.lastname: Willemsen
authors.forename: C E M Toos
authors.initials: CE
authors.lastname: van Beijsterveldt
authors.forename: Cornelius B
authors.initials: CB
authors.lastname: Lambalk
authors.forename: Grant W
authors.initials: GW
authors.lastname: Montgomery
authors.forename: Dorret I
authors.initials: DI
authors.lastname: Boomsma
mesh_terms: D000293:Adolescent; D000328:Adult; D001823:Body Composition; D004522:Educational Status; D005260:Female; D020073:Gravidity; D006801:Humans; D008423:Maternal Age; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D011247:Pregnancy; D011248:Pregnancy Complications / Q000453:epidemiology*; D015995:Prevalence; D012042:Registries; D012189:Retrospective Studies; D012307:Risk Factors; D012907:Smoking / Q000453:epidemiology*; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic; D055815:Young Adult