Many factors of a child's birth and the condition of the newborn are linked to the future development of autism, but no single factor has been identified as the cause, a meta-analysis of forty previously published research studies concludes.
Autism refers to a cluster of neurological developmental disorders, ranging to mild and severe, that interfere the child's ability to adjust normally, including defects in normal communication and social interaction.
The systematic review, published in Monday's issue of Pediatrics,  presented the results of a meta-analysis of over sixty perinatal and neonatal risk factors associated with autism reported in the forty published studies.  It identified sixteen that were  significantly associated with autism. These included low birth weight, complications associated with delivery, fetal distress during labor, "poor condition" of the newborn along with a low Apgar score, multiple births, birth injuries to the baby, and hemorrhaging of the mother during childbirth.
However,  the review found that often these factors are linked; not occurring independently but in combination, making the effect of any one factor difficult to determine. Further, the conclusions of the studies often were in conflict with each other regarding the relationship of any  single one of the factors to autism. The researcher concluded there was "insufficient evidence to implicate any one perinatal or neonatal factor in autism etiology." However, they said some evidence suggested the presence of  "multiple neonatal complications may increase autism risk."
—Study's authorsThe review also ruled out some factors, finding some were not linked to autism such as the use during childbirth  of anesthesia, forceps delivery or vacuum extractor delivery. High birth weight and  large head circumference of the newborn were also discounted.
The researcher who headed the study, Hannah Gardener, who was at the Harvard School of Public Health at the time and is now at the University of Miami School of Medicine, emphasized in an interview that parents should not worry if any one of the factors was present at the time of their child's birth. 
—Hannah Gardener, researcherShe said, "There is no single strong cause of autism." 
Twin studies have concluded that there is a genetic component to autism and Gardener emphasized the importance of  the review's conclusions that point to the need for continuing study of how factors surrounding birth may interact with genetic factors to result in future autism in a child.

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No single cause of autism, research review concludes