Interpregnancy Interval and Autism Spectrum Disorders among California Siblings in the CHARGE Study Open Access

Hutchings, Isabelle Anna (2014)

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Autism Spectrum Disorders (ASDs) have a significant health burden characterized by deficits in social skills and communication, repetitive behaviors, and stereotyped body movements usually beginning in early childhood. Short interpregnancy interval (≤ 12 months) has been associated with an increased risk of Autism Spectrum Disorders (ASDs) in previous birth-registry studies of sibling pairs. These studies, however, had limited ability to adjust for potential confounders.

ASDs were measured among California-born, singleton, full-sibling pairs in a case-control study. General population controls were selected from California birth files using stratified random sampling. Trained researchers collected information for index children for ASDs diagnoses using the Autism Diagnostic Interview-revised (ADI-R) and the Autism Diagnostic Observation Schedules (ADOS). They also used a variety of in-person and phone-based interviews to collect information on potential confounders from the index children's primary caregivers. Interpregnancy interval was defined as the time between the birth of a prior child and the conception of the index child in a full sibship. It was calculated based on information collected during interviews with the primary caregiver of the index child. Odds ratios were estimated by fitting logistic regression models.

This study included 499 singleton, full sibling pairs born in California, 265 cases and 234 controls. The OR for ASDs in the index child comparing IPI ≤ 12 months adjusting for mother's age at conception of the index child, race, education, marital status, birthplace, desire to get pregnant, procedures used to conceive the index child, prenatal vitamin use in the first month of pregnancy of the index child, family home ownership, child's gender and preterm birth was 2.0 (95% CI 1.2-3.6).

This analysis found an increased odds of ASDs among births ≤ 12 months apart, consistent with previous studies. Due to the extensive data gathered by interviewing primary caregivers, this study was able to control for a variety of potential confounders that had not previously been examined.

Table of Contents

Chapter One...3

Introduction and Background...3
IPI and ASDs...9

Chapter Two...12


Table 1...22
Table 2...24
Appendix A. IRB Letter of Approval...25

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