title: Increased risk of autism spectrum disorders at short and long interpregnancy intervals in Finland.
abstract: OBJECTIVE
  Both short and long interpregnancy intervals (IPI) are believed to present possible adverse conditions for fetal development. Short IPI has recently been associated with increased risk of autism, but whether long IPI increases risk for autism spectrum disorders (ASD) has not been thoroughly investigated. We investigated the association between short and long IPI in a Finnish population-based study.
  
  
  METHODS
  This study was conducted in the Finnish Prenatal Study of Autism, which is based in a national birth cohort. Children born in Finland in 1987 to 2005 and diagnosed with ASD by 2007 were identified through the Finnish Hospital Discharge Register. A total of 2,208 non-firstborn patients with ASD and 5,163 matched controls identified from the Finnish Medical Birth Register were included in the primary analysis. The association between IPI and ASD was determined using conditional logistic regression and adjusted for potential confounders.
  
  
  RESULTS
  Relative to births with an IPI of 24 to 59 months, those with the shortest IPI (<12 months) had an increased risk of ASD (odds ratio [OR] = 1.50, 95% CI = 1.28, 1.74) in confounder-adjusted models, whereas the ORs for longer IPI births (60-119 months and ≥120 months) were 1.28 (95% CI = 1.08, 1.52) and 1.44 (95% CI = 1.12, 1.85), respectively.
  
  
  CONCLUSIONS
  This study provides evidence that risk of ASD is increased at long as well as short IPI.
authors.affiliation: Columbia University Mailman School of Public Health, New York. Electronic address: kc2497@columbia.edu.
authors.forename: Keely
authors.initials: K
authors.lastname: Cheslack-Postava
authors.affiliation: University of Turku, Turku, Finland.
authors.forename: Auli
authors.initials: A
authors.lastname: Suominen
authors.affiliation: University of Turku, Turku, Finland.
authors.forename: Elina
authors.initials: E
authors.lastname: Jokiranta
authors.affiliation: University of Turku, Turku, Finland.
authors.forename: Venla
authors.initials: V
authors.lastname: Lehti
authors.affiliation: Columbia University Mailman School of Public Health, New York.
authors.forename: Ian W
authors.initials: IW
authors.lastname: McKeague
authors.affiliation: University of Turku, Turku, Finland; University Hospital of Turku; College of Physicians and Surgeons of Columbia University, New York State Psychiatric Institute, New York, NY.
authors.forename: Andre
authors.initials: A
authors.lastname: Sourander
authors.affiliation: Columbia University Mailman School of Public Health, New York; College of Physicians and Surgeons of Columbia University, New York State Psychiatric Institute, New York, NY.
authors.forename: Alan S
authors.initials: AS
authors.lastname: Brown
mesh_terms: D000293:Adolescent; D000067877:Autism Spectrum Disorder / Q000453:epidemiology*; D001721:Birth Intervals / Q000706:statistics & numerical data*; D002648:Child; D002675:Child, Preschool; D005260:Female; D005387:Finland / Q000453:epidemiology; D006801:Humans; D008297:Male; D012042:Registries / Q000706:statistics & numerical data*; D012306:Risk; D013997:Time Factors
keywords: autism; autism spectrum disorders; birth spacing; interbirth interval; interpregnancy interval