My DD had this at the 20 week scan. It was gone by the time she was born and didn't affect her in any way. You will probably get a follow up scan for it. The thing they worry about with it is downs syndrome. But i think thats only if they find something else with it. For eg, DD had an echogenic focus and only a 2 vessel umbilical cord(theres meant to be 3) so i had another scan just to rule out downs. Needless to say, she's a perfectly healthy 2 year old. Usually it is gone by the time they are born, if not then by the time they are 5 i think.