A preliminary study based on more than a half-million California children has found a connection between autism and having a child very near to a previous birth.
The study says children born less than two years after their siblings are considerably more likely to have an autism diagnosis compared to those born after at least three years.
The sooner the second child was conceived the greater the likelihood of that child later being diagnosed with autism.
Senior author Peter Bearman of Columbia University says the researchers took into account other risk factors for autism like age of the parents and still saw the effect.
Closely spaced births are increasing in the United States.
The study appears in the journal Pediatrics just days after a new report further tarnished a British researcher's 1998 paper linking vaccines to autism.
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