I hope that this does not spread, because it would be too bad if parents avoided another measure of standard medical care that could be lifesaving because of specilation, anecdote an coincidence. Possiblity can be at the farest end of probablity, all kinds of improbable things are possible, but not worthy of anxiety.
Causality for a complicated condition like autism is not going to be as simple as one procedure (that almost everyone has at a "suspect" time) Even if there is a correlation, that is a long way from a cause, and may mean nothing more than nearly every child who is born today has been subject to ultra sound, the mulitple reasons for a preganacy to need multiple ultrasound makes the correletaion that much more suspect. The point of reputable research is to tease out all the coincidetal and anedotal evidence and get real, repeatable results that will eventially lead to an answer that is based on all the evidence. By guessing at one single coincidence, it is like feeling the tail of the elephant blindlfolded and making an ID.
Dont waste your time worrying about this, even if you think you see a "cause" in the anedotes you collect, your child will still have a 1 in 110 risk of developing autsim just by being born. It is now 1 in 99 if your child is a boy. It is human nature to try and find someone or something to blame, and the fear of the unknown feeds people to try to find a way to prevent this outcome. You can't. If it effects your family, it won't go away if you can blame something as cause and treatment are not linked either, and even if you get to the point where you feel strongly about who the "guilty" party is, you will not feel any better about it if your child is autistic; in some cases, I think people feel worse if they can vent about something that they think hurt thier child, you are much better equiped if you can move forward instead. I think this trend even leads parents to more self blame and guilt, because they start to beleive that they should have prevented it.
If you are still seeking anecdote, my 18 year old had one ultrasound, and is autistic. She also went to the circus, ate chicken, peas, pears, bananas, stubbed her toe, was sung to, had stiches, and many other shared childhood expereinces, but I choose to accept the unknown and our genetics as the cause, which is why she is participating the the Autism gene research project, AGRE. They just annouced a break through genetic discovery this week, and you would be much better off reading about that, and joining the project if you turn out to be one of the few for whom autism is reality, than you will be to look to speculation and unecessary worry.
Keep your blood pressure low by refusing to buy into this and think possitive thoughts about your pregnancy and know what the developmental milestones are, never wait and see if you think you have a problem, and get the earliest intervention that you can muster or afford if your child is one of the 1 in 110. You don't have to think about that today, and you might want to read trashy magazines instead of seaching the internet until your baby is born, just to keep your blood presure down!
Good luck with your new baby and enjoy being Mommy to number #1.
M.