Key Findings: Population Attributable Fractions for Three Perinatal Risk Factors for Autism Spectrum Disorders, 2002 and 2008 Autism and Developmental Disabilities Monitoring Network

The Annals of Epidemiology journal has published a new study that focuses on pregnancy-related factors that might put children at risk for autism spectrum disorder (ASD). Researchers from CDC and the Autism and Developmental Disabilities Monitoring (ADDM) Network found that 12-13% of ASD among children in multiple U.S. communities was related to being born too early, too small, and/or by Cesarean delivery. Researchers can use this new information to inform future studies looking at other factors that put children at risk for ASD and how those factors contribute to the overall burden of ASD among large groups of children.

You can read the article’s abstract here. Read more below for a summary of the findings from this study.

Main Findings from this Study

• Overall, between 12-13% of ASD among children in multiple U.S. communities was related to being born too early, too small, and/or by Cesarean delivery. In other words, if it were possible to eliminate the many different reasons children are born too early, too small, and/or delivered by Cesarean, the number of children with ASD would be reduced by 12-13%.
  • For children born in 1994:
    • About 4% of ASD was related to being born too early, 1% to being born too small, and 8% to being born by Cesarean delivery.
  • For children born in 2000:
    • About 2% of ASD was related to being born too early, 3% to being born too small, and 7% to being born by Cesarean delivery.
  • There were no notable differences when comparing children born in 1994 with those born in 2000.
• There are multiple, complex reasons for being born too early, too small, and/or by Cesarean delivery. This study examined these three factors because they are relatively common and thus could contribute to the overall burden of ASD among large groups of children. While each of the factors studied has been linked with an increased risk for ASD in numerous past studies, the exact causes of these relationships between the factors and the risks for ASD are still not well understood.
  • For example, there are many different reasons a woman might have a Cesarean delivery. Perhaps the Cesarean delivery itself directly affects children’s risk for ASD. Alternatively, the increased risk of ASD could be because of certain health conditions affecting either the mother or child, which then resulted in the need for a Cesarean delivery.  Therefore, more work needs to be done to understand this observed relationship between Cesarean delivery and the increased risk for ASD.
• Taken together, the results from this study highlight the role that certain experiences before and during pregnancy play in putting children at risk for ASD.
• Researchers can use this new information to inform future studies looking at other factors that put children at risk for ASD and how those factors contribute to the overall burden of ASD among large groups of children.
  • It is important to note that these findings tell us more about how these pregnancy-related factors impact ASD risk for groups of children as a whole and not for individual children. This new information should not be used to make recommendations for clinical practice.

About this Study

This study used data collected by several sites in the ADDM Network. Specifically, it looked at information from white, black, and Hispanic children born in 1994 or 2000 in parts of Alabama, Arizona, Arkansas, Georgia, Maryland, Missouri, North Carolina, and Utah. Researchers chose to examine data on children born in 2000, our most recent available data, and compare it with data from an earlier time. Researchers estimated the average population attributable fraction (see below) for those children that were born too early (less than 37 weeks), born too small (less than 10^th percentile), and/or born by Cesarean delivery. A population attributable fraction measures the contribution of a specific factor to the development of a certain disease or condition. For example, it addresses the hypothetical question, “If preterm delivery was eliminated, what impact would that have on the number of children with ASD?” This study used a more in depth method for calculating population attributable fractions than most other studies. This method takes into account some of the key limitations of other methods. In particular, this method allows for consideration of multiple related factors at the same time.

Reference for Key Findings Feature

Schieve LA, Tian LH, Baio J, Rankin K, Rosenberg D, Wiggins L, Maenner MJ, Yeargin-Allsopp M, Durkin M, Rice C, King L, Kirby RS, Wingate MS, Devine O. Annals of Epidemiology. January 2014. [epub ahead of print]

Autism Spectrum Disorder: CDC Activities

CDC is committed to continuing to provide essential data on ASD, to search for risk factors and causes of ASD, and to develop resources for parents and professionals that help identify children with ASD and other developmental disabilities as early as possible.

To download developmental milestone checklists and other free materials for parents, healthcare providers, and early childhood educators, please visit Learn the Signs. Act Early website.

To learn more about autism spectrum disorder, please visit autism website.