Low Birth Weight and Prematurity Raises Risk of Autism

Low birth weight is one risk factor for autism

mother holdind hand of a premature baby in incubator
Christian Wheatley/E+/Getty

Low Birth Weight Increases Risk of Autism -- Though Risk Remains Low

In June of 2008, the U.S. Centers for Disease Control and Prevention released a study linking autism and low-birth rate that caused a bit of a stir among the news media. Another 2013 study confirmed the finding.

Unfortunately, while the media did report correctly on the findings, they picked out only the most sensational bits to share with the public.

A Fox News article, for example, made the statement "The study found that boy's born at a birth weight of lower than 5.5 pounds had a 2.3-fold increased risk for autism. Girls had a three times or even a higher risk for developing autism." Fox was right - but there's much more to the story.

While the risk of autism does rise for preemies, it actually rises less than the risk for many other developmental disorders. In part, here's what the actual study abstract says:

  • The prevalence of autism in low birth weight or preterm children was markedly lower than those of other developmental disabilities. In multivariate analyses, birth weight of <2500 g and preterm birth at <33 weeks' gestation were associated with an approximately twofold increased risk for autism, although the magnitude of risk from these factors varied according to gender (higher in girls) and autism subgroup (higher for autism accompanied by other developmental disabilities). For example, a significant fourfold increased risk was observed in low birth weight girls for autism accompanied by mental retardation, whereas there was no significantly increased risk observed in low birth weight boys for autism alone.

    In other words, while low birth weight does, in fact, present a risk factor for autism, the risk is much LESS than that of developing cerebral palsy, cognitive challenges, hearing loss, or vision impairment.

    Reasons for the Association Between Low Birth Weight and Autism Are Elusive

    In fact, the most significant finding in this study, it seems, is that the risk of autism, specifically, for low-weight baby girls, is far greater than the risk of autism, specifically, for low-weight boys.

    So far, no one knows why the risk of autism for preemies is LESS than the risk of other problems - nor why the risk of autism for girl preemies is GREATER than that for boy preemies.

    A related article in US News and World Reports cites the researchers:

    "This gives us more clues [about autism], which we desperately need, but it's not anything clinicians can use right away," said Dr. Cindy Molloy, an autism researcher and clinical assistant professor of pediatrics at the Center for Epidemiology and Biostatistics at Cincinnati Children's Hospital.

    The results do reinforce the importance of monitoring children who are born underweight or early for behavioral problems so they can be treated, said study author Diana Schendel, lead health scientist at the CDC's National Center on Birth Defects and Developmental Disabilities.

    This study's findings support a prior small study which came to similar conclusions. After screening 91 ex-preemies, researchers at McGill University note in the abstract of their paper in Pediatrics:

    • Early autistic behaviors seem to be an underrecognized feature of very low birth weight infants. The results from this study suggest that early screening for signs of autism may be warranted in this high-risk population followed by definitive autism testing in those with positive screening results.

      Bottom line: low birth weight babies should be carefully monitored for developmental problems. Those problems may include autism, though autism is LESS likely than other, more common problems.


      Leavey A1, Zwaigenbaum L, Heavner K, Burstyn IGestational age at birth and risk of autism spectrum disorders in Alberta, Canada. J Pediatr. 2013 Feb;162(2):361-8.

      Limperopoulos C, Bassan H, Sullivan NR, Soul JS, Robertson RL Jr, Moore M, Ringer SA, Volpe JJ, du Plessis AJ. Positive screening for autism in ex-preterm infants: prevalence and risk factors. Pediatrics. 2008 Apr;121(4):758-65.

      Schendel D, Karapurkar Bhasin T.

      MPH Birth Weight and Gestational Age Characteristics of Children With Autism, Including a Comparison With Other Developmental Disabilities. Pediatrics Vol. 121 No. 6 June 2008, pp. 1155-1164.