Need answers! Nuchal Translucency scan

At what stage (wk) did you have NT scan, I realise this is usually referred to as '12 week scan' my dr has encouraged me to get it done now, currently 11wks 3 days. I'm wanting to wait for another week or so to do the scan. Does the scan get clearer or provide a better reading if I wait?

With my first pregnancy I had an early reading right on 12 weeks and they said baby had an 85% chance of DS, delivered healthy and no DS with first but it was still very traumatic and I would like to avoid that if possible this time.