title: The effect of birth order and parental age on the risk of type 1 and 2 diabetes among young adults.
abstract: OBJECTIVE
  The aim of this study was to examine the effects of birth order and parental age on the risk of type 1 and type 2 diabetes among Finnish individuals aged 15-39 years.
  
  
  METHODS
  Data on all cases of type 1 diabetes (n = 1,345) and type 2 diabetes (n = 1,072), diagnosed between 1992 and 1996, were collected from four sources: standardised national reports from diabetes nurses, the National Hospital Discharge Register, the Drug Prescription Register and the Drug Reimbursement Register. Information on matched controls and the family members of all study subjects were obtained from the National Population Registry. The odds ratios (ORs) for both types of diabetes were estimated using a conditional logistic regression model.
  
  
  RESULTS
  There was a U-shaped relationship between maternal age and the risk of type 2 diabetes in the offspring: the risk was higher in children born to young and old mothers compared with children born to mothers aged around 30 years. The children born second (OR 0.76, 95% CI 0.62-0.94), third (OR 0.73, 95% CI 0.55-0.95), or fourth (OR 0.66, 95% CI 0.47-0.94) had a lower risk of type 2 diabetes than the first-born children. Maternal age, paternal age, and birth order did not have an effect on the risk of type 1 diabetes in the individuals aged 15-39 years at the time of diagnosis.
  
  
  CONCLUSIONS
  Maternal age and birth order are both associated with the risk of early-onset type 2 diabetes. However, part of these associations may be due to low birthweight. In this study neither parental age nor birth order showed a significant association with the risk of type 1 diabetes diagnosed after 15 years of age.
authors.affiliation: Diabetes Unit, Department of Health Promotion and Chronic Disease Prevention, National Public Health Institute, Helsinki, Finland. niina.lammi@helsinki.fi
authors.forename: N
authors.initials: N
authors.lastname: Lammi
authors.forename: E
authors.initials: E
authors.lastname: Moltchanova
authors.forename: P
authors.initials: P
authors.lastname: Blomstedt
authors.forename: J G
authors.initials: JG
authors.lastname: Eriksson
authors.forename: O
authors.initials: O
authors.lastname: Taskinen
authors.forename: C
authors.initials: C
authors.lastname: Sarti
authors.forename: J
authors.initials: J
authors.lastname: Tuomilehto
authors.forename: M
authors.initials: M
authors.lastname: Karvonen
mesh_terms: D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D001722:Birth Order; D003922:Diabetes Mellitus, Type 1 / Q000453:epidemiology / Q000209:etiology*; D003924:Diabetes Mellitus, Type 2 / Q000453:epidemiology / Q000209:etiology*; D006801:Humans; D010290:Parents; D012042:Registries; D012307:Risk Factors