Low birth weight may increase a person's chances of developing autism, according to a study in the November Pediatrics. More than 600 children who were born in the mid-1980s weighing 4.4 pounds or less were followed until age 21. The researchers found that 5 percent of them had autism spectrum disorder diagnoses, a rate five times that found in the general American population. Also, the lower the birth weight, the higher the likelihood of an autism diagnosis.