title: Interpregnancy Interval and Risk of Autism Spectrum Disorders.
abstract: OBJECTIVE
  To determine whether subsequent births after short and long interpregnancy intervals (IPIs) are associated with risk of autism spectrum disorder (ASD).
  
  
  METHODS
  We assessed the association between IPI and ASD risk in a cohort of 45 261 children born at Kaiser Permanente Northern California (KPNC) between 2000 and 2009. Children with ASD were identified from International Classification of Diseases, Revision 9 diagnostic codes 299.0, 299.8, and 299.9 recorded in KPNC electronic medical records. IPI was defined as the time from the birth of the first child to the conception of the second child. Survival analysis and logistic regression models were used to evaluate the association between IPI and risk of ASD in second-born children.
  
  
  RESULTS
  Children born after an IPI of <12 months or ≥72 months had a 2- to 3-fold increased ASD risk compared with children born after an interval of 36 to 47 months. Respective adjusted hazard ratios (95% confidence intervals) were as follows: <6 months, 3.0 (1.9-4.7); 6 to 8 months, 2.1 (1.4-3.3); 9 to 11 months, 1.9 (1.3-2.1); 12 to 23 months, 1.5 (1.1-2.1); and ≥72 months, 2.4 (1.5-3.7). The results are not explained by maternal BMI or change in BMI between pregnancies or by parental age, maternal antidepressant medication use, or unfavorable events occurring during the first or second pregnancy.
  
  
  CONCLUSIONS
  Children born after interpregnancy intervals <2 years or >6 years may be at increased risk of ASD. The mechanism explaining this association is unknown, and more research is needed.
authors.affiliation: Division of Research, Kaiser Permanente Northern California, Oakland, California; and ousseny.x.zerbo@kp.org.
authors.forename: Ousseny
authors.initials: O
authors.lastname: Zerbo
authors.affiliation: Division of Research, Kaiser Permanente Northern California, Oakland, California; and.
authors.forename: Cathleen
authors.initials: C
authors.lastname: Yoshida
authors.affiliation: Division of Research, Kaiser Permanente Northern California, Oakland, California; and.
authors.forename: Erica P
authors.initials: EP
authors.lastname: Gunderson
authors.affiliation: Department of Obstetrics and Gynecology, Kaiser Permanente Northern California, San Francisco, California.
authors.forename: Kaht
authors.initials: K
authors.lastname: Dorward
authors.affiliation: Division of Research, Kaiser Permanente Northern California, Oakland, California; and.
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Croen
mesh_terms: D000293:Adolescent; D000067877:Autism Spectrum Disorder / Q000453:epidemiology*; D001721:Birth Intervals; D002648:Child; D005260:Female; D006801:Humans; D008297:Male; D018570:Risk Assessment; D012307:Risk Factors