Preterm Births Increase Risk of ADHD and Autism

Understanding the factors contributing to the prevalence of ADHD and autism requires examining the type and magnitude of risk factors for the disorders.  One risk factors common to both disorders is early or pre-term birth.  Advances in neonatal care dramatically increase survival in infants born as early as the fifth or sixth month of pregnancy.

A recent study published in the journal Pediatrics provides some important new data about the risk of ADHD in pre-term birth infants.  Scientists in Sweden examined the prevalence rates for ADHD in a group of children born preterm and compared it to the rates in infants born at term or slightly later.  Using several statistical models, they estimated the magnitude of effect of preterm birth on ADHD.  They found a significant statistical effect--the earlier the birth in gestation the greater the likelihood of childhood ADHD.

The magnitude of this effect is an approximate doubling of the risk for the earliest births.  The data from the study (model 3) estimated the risk (odds ratio) of childhood ADHD at several stages of development at birth:

• 23-28 weeks  Odds ratio=2.1
• 29-32 weeks  Odds ratio=1.6
• 33-34 weeks  Odds ratio=1.4
• 35-36 weeks  Odds ratio=1.3
• 37-38 weeks  Odds ratio=1.1
• > 38 weeks    Odds ratio=1.0

Similar studies in autism and autism spectrum disorder estimated a similar magnitude of risk for autism and autism spectrum disorder in preterm birth.  Infants born before 30 weeks appear to have approximately a doubled risk for autism and ASD.

From a prevention viewpoint, these studies support efforts to reduce the risk of preterm birth.  Although it is impossible to eliminate preterm births, the following measures can significantly reduce the risk:

• Smoking cessation during pregnancy
• Early and regular prenatal care
• Reducing the number of multiple birth pregnancies in infertility couples
• Progesterone use in women with a previous history of preterm birth
• Reducing the number of pregnancy inductions and C-sections in preterm pregnancies

Increased number of viable preterm births may be contributing to a portion of the number of children with ADHD and autism/autism spectrum disorders.  Improved neonatal care of preterm infants carries the potential for more children with special needs.  Improving neonatal care for infants in the neonatal intensive care as well as public health efforts to reduce the number of preterm births are critical initiatives for prevention of ADHD and autism.

The March of Dimes has an online resource site that provides professional education of the issue of reducing preterm births.

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Lindstrom, K., Lindblad, F., & Hjern, A. (2011). Preterm Birth and Attention-Deficit/Hyperactivity Disorder in Schoolchildren PEDIATRICS DOI: 10.1542/peds.2010-1279

Schendel D, & Bhasin TK (2008). Birth weight and gestational age characteristics of children with autism, including a comparison with other developmental disabilities. Pediatrics, 121 (6), 1155-64 PMID: 18519485