A recent study funded in part by Autism Speaks and just published in the Journal of Autism and Developmental Disorders examined whether there is a relationship between autism and exposure to prenatal ultrasound scans. The investigators found no differences in the number of ultrasounds received by the mothers who had a child diagnosed with autism and those whose child did not receive a diagnosis. The lack of association was seen even when the data was analyzed by trimester. The investigators made use of a widely used health care system to identify children and age-matched controls for comparison, and therefore were able to capture a large number of cases and controls for this study.
An abstract of the publication can be found here.