According to researchers from Manchester University, extreme birth weights (small and large) may be a risk factor for autism. This is the first study, to the knowledge of study authors) that links larger birth weight infants with autism risk. The study was published in the American Journal of Psychiatry. 

Researchers pulled information for the study from more than 580,000 child health records. After eliminating certain children due to age and other factors, about 40,000 health records were used. All original health records were for children between 0 and 17, but only children old enough to be diagnosed with autism spectrum disorder were included in the study. 

Based on records, about 4,200 children in the cohort were diagnosed with autism. These records were compared to more than 36,000 children who were not diagnosed with the condition. According to health records, infants weighing more than 9 lb 14 oz and less than 5 lb 8 oz were at increased risk of autism. Low birth weight was associated with an overall risk of 63% whereas high birth weight was associated with an overall risk of 60%. Risk factors were independent of pre-term or post-term delivery in cases of higher birth weight. 

According to study author Kathryn Abel, abnormal fetal growth appears to be the connection. “We think that this increase in risk associated with extreme abnormal growth of the fetus shows that something is going wrong during development, possibly with the function of the placenta.” If the placenta is functioning abnormally it could be causing issues with brain development, thus the increased risk of autism in smaller than average and larger than average infants. 

The size of the study pool lends validity to the study results, which could lead to additional large cohort studies across the world. Researchers are constantly on the lookout for definitive causes of autism. To date, there are no definitive causes or cures for the disorder. 


Source: Catherine Lord. Fetal and Sociocultural Environments and Autism. American Journal of Psychiatry, 2013; 170 (4): 355 DOI: 10.1176/appi.ajp.2013.13010078