I had recently (33+6) and it's just a scan to measure baby, they do the head circumference, abdominal circumference, femur length, and I think they measure other bits too, to get a rough estimate of baby's size and weight.
Our lil man weighed 5lb at 33+6 which the consultant said is great! I now don't have to have anymore as my pregnancy now seems 'normal'. I was having the growth scans because I had severe preeclampsia and our daughter had IUGR, all is going perfectly for now though and I'm excited to hopefully, have a term baby! Xx