Birth Weight May Influence Severity and Risk of Autism Spectrum Disorders

Approximately 1% of children are born with an autism spectrum disorder (ASD), which is a neurological condition that affects a range of behavioral and cognitive domains. Studies on ASD have focused on risk factors including maternal stress, parental age, environmental influences, and genetics. One potential risk factor that has also been looked at is birth weight. However, the relationship between birth weight and predisposition for ASD is still unclear. Some research involving twins has suggested a higher risk for ASD among monozygotic twins (MZ) or identical twins rather than dizygotic (DZ) or fraternal twins. This could be due to the totality of shared genetics among MZ versus DZ twins. In these studies and studies involving single births, birth weight has been linked to ASD.

To get a better picture of how birth weight affects risk and severity of ASD, Molly Losh of the Roxelyn and Richard Pepper Department of Communication Sciences and Disorders at Northwestern University in Illinois led a study on both MZ and DZ twins. She evaluated parent reports of ASD severity and compared the birth weights of over 3,700 same-sex twin sets that were part of the Child and Adolescent Twin Study of Sweden (CATSS).

Losh found that the low-birth-weight twins had a threefold increased risk for ASD than twins with heavier birth weights. She also discovered that every 100-gram weight increase resulted in a risk reduction of 13%. Additionally, the increased birth weights also correlated with decreases in symptom severity of spectrum disorders including attention-deficit hyperactivity disorder (ADHD). The results also revealed a clear link between birth weight and isolated deficits. Specifically, the twins with the lowest birth weights were more likely to have language and social impairments than problems with repetitive actions like tapping or rocking. Losh said that although genetic effects were very important, there might be a nongenetic influence associated with birth weight that contributes to the development of ASD.

Losh, M., Esserman, D., Anckarsater, H., Sullivan, P. F., Lichtenstein, P. (2012). Lower birth weight indicates higher risk of autistic traits in discordant twin pairs. Psychological Medicine, 42.5, 1091-1102.

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  • Anna Rush S

    Anna Rush S

    May 25th, 2012 at 6:29 PM

    Now that’s a theory that I haven’t heard before.
    If we know that lower birth weights tend to produce more brith defects as well as more behavioral and acandemic problems later in life, then today is the day that we have to take those necessary steps to advocate for full term pregnancies and ending the rash of premature births that seem to continually plague us. The research is there, the education is there, now we just have to put it into action all across the board.

  • ruth


    May 26th, 2012 at 12:16 AM

    low birth weight often carries the risk of many things.I have heard of this before but not with relation to autism. If there s a new born with low weight then it makes sense to go through a variety of checks and tests to ensure the baby will not have health complications because there seems to be a big risk for such babies.

  • armstrong


    May 26th, 2012 at 3:57 AM

    I do believe that this could play a role in autism; howeverI don’t want parents to forget that there is also some very strong evidence that environmental factors can play a role as well. Think about that very hard before considering the vaccines that you allow doctors to give your children. Weigh the risks of cleaning products that you use in your home. Educate yourself about the foods that you feed to your children. I know that there are those who poo poo this evidence but there is enough of it out there to be compelling to believe. None of us really have the answer, but don’t close your eyes to the suggestions that are out there, because you just don’t know which one could affect your own child.

  • norris


    May 26th, 2012 at 4:58 AM

    now almost all twins and triplets are prone to have a low birth weight.does that make them any more vulnerable to ASD than single children?

  • claudia


    May 26th, 2012 at 6:22 PM

    my son is very mild but he weighed 8lbs. He nursed until he was almosy 24 months and has mostly eaten organic food. There is no Autism in either my husband’s or my side of the family,although we probably both have undiagnosed adhd(which I suspect is in the Spectrum) Oh,and he was vaccinated.

  • Georgia


    May 28th, 2012 at 4:38 AM

    I caution moms to be careful in the reading, as this says that it could influence the risk of asd but does not cause it. By no means should you think that just because you may have had a low birth rate baby that he or she is certain to develop symptoms of autism. But it should cause us to think about how we are treating ourselves and our fetus throughout our pregnancy and make sure that we are doing all the right things that will help us carry that child to full term so that this will increase the likelihood that the baby won’t be st any sort of increased risk for the development of asd or other illnesses like it.

  • Rodney


    May 29th, 2012 at 4:07 AM

    I have an autistic son and nobody has ever mentioned this to me, not even our pediatrician. Why? Is this something new? Not that it could change things now, but maybe had this been stressed more then we could have done something different when my wife was pregnant? The only thing that I don’t want to see come of all of this is for the finger pointing to start. You know, you can’t say things like “well of you had done this or that then this would not have happened to him.” We as a family have played the blame game, but the fact of the matter is that this only tears you apart and does nothing to fix the real problem.

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