title: The association between the interpregnancy interval and autism spectrum disorder in a Canadian cohort.
abstract: OBJECTIVE
  Two studies reported an increased risk of autistic disorder in children conceived less than 12 months after a previous birth. Our objective was to examine the association between the interpregnancy interval (IPI) and autism spectrum disorder (ASD) in a Canadian cohort.
  
  
  METHODS
  Using administrative datasets housed at the Manitoba Centre for Health Policy, we identified pairs of first- and second-born singleton siblings born between 1988 and 2005. Diagnoses of ASD were ascertained by searching physician billing claims, hospital discharge abstracts, education data, and a database containing information on individuals identified for a 2002-2007 ASD surveillance program in Manitoba. Logistic regression models were fit to examine the association between the IPI and ASD in 41,050 second-born siblings where the first-borns did not have ASD, using IPIs of ≥ 36 months as the reference category and specifying three case groups. Case Group 1 included individuals with at least one ASD code (n = 490); Case Group 2 included those with two or more ASD codes (n = 375); and Case Group 3 comprised individuals with a record in the ASD surveillance program database (n = 141).
  
  
  RESULTS
  The adjusted odds ratios (ORs) for IPIs shorter than 12 months ranged from 1.22 (95% CI: 0.91-1.63) for Case Group 1 to 1.72 (95% CI: 0.96-3.06) for Case Group 3. When the case groups were restricted to individuals with more severe ASD, the ORs increased and were significant for Case Groups 1 and 2.
  
  
  CONCLUSIONS
  Our findings also support an association between short IPIs and more severe ASD.
authors.forename: Helen
authors.initials: H
authors.lastname: Coo
authors.affiliation: Queen's University. oullette@queensu.ca.
authors.forename: Hélène
authors.initials: H
authors.lastname: Ouellette-Kuntz
authors.forename: Yuk-Miu
authors.initials: YM
authors.lastname: Lam
authors.forename: Marni
authors.initials: M
authors.lastname: Brownell
authors.forename: Michael P
authors.initials: MP
authors.lastname: Flavin
authors.forename: Leslie L
authors.initials: LL
authors.lastname: Roos
mesh_terms: D001721:Birth Intervals / Q000706:statistics & numerical data*; D002170:Canada / Q000453:epidemiology; D002648:Child; D002659:Child Development Disorders, Pervasive / Q000453:epidemiology*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D018570:Risk Assessment; D012720:Severity of Illness Index; D013997:Time Factors
keywords: Autism; Manitoba Centre for Health Policy; administrative data; interpregnancy interval; record linkage; secondary analysis