The association between the interpregnancy interval and autism spectrum disorder in a Canadian cohort

Helen Coo, Hélène Ouellette-Kuntz, Yuk-Miu Lam, Marni Brownell, Michael P. Flavin, Leslie L. Roos


OBJECTIVES: 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.

CONCLUSION: Our findings also support an association between short IPIs and more severe ASD.


Autism; interpregnancy interval; secondary analysis; administrative data; record linkage; Manitoba Centre for Health Policy

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