At my 12 week scan the sonographer asked if I wanted the blood test for downs & Edwards & Pataus. I said yes but was visibly anxious and she said why don't I leave it as it might worry me more. She said I could have it at 20 weeks anyway.
Then when I got to 20 wk scan they said I'd missed the screening.
I've no reason to suspect I'm high risk and no markers or problems have came up at any of the scams.
Just wondering if it would likely have been picked up at the ultrasound? They said all scams have been great, no problems, but it's nagging at the back of my mind worrying me 
Are there any non invasive tests I could ha d at this stage (24 weeks). If it was Downs we would still obviously want the baby but the other two sound a lot more serious.