Length of Time Between Births May Increase Autism Risk

Second-born children who are conceived sooner than two years or later than six years after the arrival of their older sibling have a substantially increased risk of autism spectrum disorder (ASD), according to a new study.

Researchers at the Kaiser Permanente Division of Research (Oakland, CA, USA) conducted a study to assess the association between interpregnancy intervals (IPIs) 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 KPNC electronic medical records, and IPI was defined as the time from the birth of the first child to the conception of the second child.

The results showed that autism was diagnosed in 0.81% of second-born children, following IPIs of three to four years. In second-born children with IPIs of less than six months, the prevalence of autism was 2.11%; for intervals of six to eight months, 1.74%; and for intervals of six years or more, 1.84%. According to the researchers, the results are not explained by maternal body mass index (BMI) or change in BMI between pregnancies, parental age, maternal antidepressant medication use, or unfavorable events occurring during the first or second pregnancy. The study was published on September 24, 2015, in the Pediatrics.

“Interpregnancy intervals—the time from the first birth to conception of the second child—may be a factor in autism risk,” said lead author Ousseny Zerbo, PhD. “And while additional research is needed, our study adds to the growing body of evidence about various risk factors for autism.”

ASD affects 6 per 1,000 children, and occurs more often among boys than girls. ASD affect three different areas of a child's life - social interaction, communication (both verbal and nonverbal), and behaviors and interests. The three main types of ASD are Asperger's syndrome, pervasive developmental disorder, not otherwise specified (PDD-NOS), and autistic disorder. The DSM-5 also included two rare but severe autistic-like conditions, called Rett syndrome and childhood disintegrative disorder.

To help determine how various autism risk factors may be linked to family genetics or environmental issues, a new effort is underway at Kaiser Permanente called the Autism Family Biobank, which will collect genetic information on a voluntary basis from 5,000 member families with a child on the autism spectrum, for a total of 15,000 participants.

Related Links:
Kaiser Permanente Division of Research
Kaiser Permanente Autism Family Biobank