Just tell them you don't want to know , if you don't know what to look for you'll be none the wiser anyway.
Thanks for all the responses. I'm not a sonographer or ultrasound reader, but do know about the stripes. Hopefully, the little one will just keep themself decent and not be too obvious. I will be going in saying 'i don't want to know.. i don't want to know...' so the scanner person knows our intentions.

Thanks again all,

Kate