That first ultrasound is a thrill for parents, but new research suggests that the practice may make autism more severe in children born with the disorder. 
Current Food and Drug Administration (FDA) guidelines state that diagnostic ultrasounds should only be conducted in cases of medical necessity, a recommendation that seems to be supported by the findings of the study.
For the study, published in the journal Autism Research, researchers at University of Washington’s (UW) Medicine school, UW Bothell, and the Seattle Children’s Research Institute, looked at the variability of symptoms in autistic children, rather than the causes of the disorder. 
The researchers culled data from the Simons Simplex Collection autism genetic repository funded by the Simons Foundation Autism Research Initiative. The data came from more than 2,600 families among 12 research sites across the United States.
Lead author Sara Webb, UW Medicine researcher in psychiatry and behavioral sciences, said:
“There has been a real struggle in why there are so many kids with autism. Where does this disorder develop from? How do kids get autism? And the second question is why are kids with autism so different from each other?
This study really looks at the second question. Within kids with autism, what are some of the factors that may result in a child having a good outcome or higher IQ or better language or less severity versus a child who maybe takes more of a hit and continues to struggle throughout their lifespan?”
The team used a 3-part model explaining variability in the children suffering with autism:
The research suggests that kids with certain autism-related genetic variations had more severe symptoms if their mothers had a 1st trimester diagnostic ultrasound.
No link was found between autism severity and 2nd or 3rd trimester ultrasounds. 
As a mother of 2, Webb said that she would opt out of having an ultrasound in the first 3 months of pregnancy unless it was absolutely medically necessary, and unless she knew exactly how far along she was in her pregnancy. She said:
“If we can figure out this information in any other way, I would go with that. It’s always worth considering that when we do medical procedures, there are great benefits but also risk.”
 Medical Daily
 Science Daily